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Intercalation in the Chinese Calendar is after the eighth month every 19 years and is called ren ba yue (Double August). According to tradition, tragedy will follow when the month is added at that time. [Gevisier] Egyptian biochemist Rashad Khalifa (19351990) claimed that he discovered an intricate numerical pattern in the text of the Qur'an involving the number 19. Sura 74:30 reads: "Over it are nineteen." In his August 1941 Afterward to Thomas Wolfe's book The Hills Beyond, NY, Wolfe's editor, Edward C. Aswell, remarks that Thomas Wolfe's second book, never published, was to have been titled K19. When Wolfe died, Aswell watched the train carrying his coffin go by. Train K19! [Haga] The smallest prime that is equal to the product of its digits plus the sum of its digits: 19 = (1 * 9) + (1 + 9). [Losnak] The Bahá'í calendar, established in the middle of the 19th century, is based on cycles of 19 years. Years are composed of 19 months of 19 days each. [Dybwad] (19  1) divides (19^{19}  1) a prime number of times. [Wagstaff] 19 is the smallest prime p such that 10*p {+ 1, 3, 7, and 9} are all primes. [Das] 19 is the smallest prime p such that p and p^{2} have the same sum of digits. The recurring decimal cycles for 1/19 to (19  1)/19 form a true magic square. Blaise Pascal deduced 19 theorems related to his famous triangle. 1111 * 111^{11} + 111111111 + 1 (19 ones) is prime. [Fougeron] A street in Rome named St. John's Lane is only 19 inches wide. The first prime repfigit number. A repfigit (repetitive fibonaccilike digit) number is an ndigit integer N with the following property: if a Fibonaccilike sequence (in which each term in the sequence is the sum of the n previous terms) is formed, with the first n terms being the decimal digits of the number N, then N itself occurs as a term in the sequence. For example, if the digits of 19 start a Fibonaccilike sequence, then 19 appears as a term: 1, 9, 10, 19. These are also known as Keith numbers. [Beedassy] The number of trailing 0's in 80!. Amendment 19 to the United States Constitution gave women the right to vote. [Filler] 19 European nations endorsed the first international ban on human cloning. 2^{1} + 3^{2} + 5^{3} + 7^{4} + 11^{5} + 13^{6} + 17^{7} + 19^{8} is prime. Product 19 is a multivitamin and mineral cereal of toasted corn, oats, wheat, and rice. The Rhind papyrus contained a problem to find x so that x plus one seventh of x will equal 19. An idiot is someone with an intelligence quotient (IQ) less than or equal to 19. [Brenner] 19 = 8 + 2 + 8 + 1, and its reversal equals the square root of 8281. Pont du Gard aqueduct in southern France was built in 19 B.C. [Feather] In golf, the clubhouse bar is referred to as the 19th Hole. 19^{5} + 19^{2} + 19^{1} + 19^{3} + 19^{5} + 19^{6} + 19^{4} + 19^{0} = 52135640. [De Geest] A gene on Chromosome 19 has been linked to Alzheimer's disease. In the game of Go, two players alternate in placing black and white stones on a large (19by19 line) ruled board, with the aim of surrounding territory. Consider a chess endgame where a King plus OppositeColored Bishops (i.e., two Bishops each residing on oppositecolored squares) versus a King. The checkmate requires, at most, 19 moves (if the side with the bishops move first). For k = 1, 2, 3, ... 19 at least one of the integers of the form 6k + 1 or 6k  1 is prime. [Crespi de Valldaura] The smallest number of neutrons for which there is no stable isotope. [Hartley] 19 divides its following consecutive concatenated composite numbers (202122). [De Geest] The largest prime on the Ishango bone. This tool (made from the fibula of a baboon) was found on the shore of Africa's Lake Edward and is believed to be at least 20000 years old. The numbers on one of its columns form a prime quadruple. It is now located on the 19th floor of the Royal Belgium Institute of Natural Sciences in Brussels. For decades, mathematicians the world over would open their doors to find the homeless Paul Erdős (19131996) announcing, "My brain is open!" It is rumored that for 19 hours a day, seven days a week, stimulated by coffee, and later by amphetamines, he worked on mathematics. One of his greatest achievements was the discovery of an elementary proof for the prime number theorem. If we pretend = 60/19, then a radius of 57 gives a circumference of exactly 360. [Moody] "The Sun" is numbered with 19 in Tarot cards. The Metonic cycle, which involves the phase cycle of the Moon, is a period of about 19 Julian years. [Gevisier] 19 is the largest prime that can be expressed pandigitally in some base b > 1 (19 = 201 in base 3). [Keith] (19^{19}  2^{19})/(19  2) is prime. [Luhn] Waring conjectured in 1770 that every positive integer can be expressed as a sum of at most 19 biquadrates (fourth powers). This was later proven by Balasubramanian, Deshouillers, and Dress. Scores of people once died from the Anthrax bacterium following an accident at "Compound 19," a Soviet military facility in the city of Sverdlovsk (now called Yekaterinburg). 19 times its reversal is the famous HardyRamanujan number. 19 is the smallest prime which is the sum of three discrete primes (3 + 5 + 11). [Mander] The smallest prime that yields another if its sum of digits is sandwiched between its digits. [Silva] Flight 19 disappeared in the Bermuda Triangle. [Leonard] The Statue of Liberty's torch shines through leaded glass, illuminated by 19 lamps. [Pitkin] Osama bin Laden has 19 brothers. [NBC News] In ancient Sweden the dates of the full moon were computed by runic calendar sticks (runstavar) with the full moon marked only at 19 fixed dates within each month. [Haga] The composer Béla Bartók finished his Opus 19 in 1919, when he was 38 (twice 19) years old; the title in his native Hungarian (A csodálatos mandarin) has 19 letters. [Ace] Steely Dan had a hit song called "Hey Nineteen." A hoax chess machine nicknamed "the Turk" once sent Napoleon Bonaparte into a fury by beating him in 19 moves. [Hsu] Inserting seventeen zeros between the two digits of 19 makes another prime of exactly 19 digits. Note that seventeen and 19 are twin primes. [De Geest] The main building of the North Dakota State Capitol is a 19story Art Deco skyscraper. It is the tallest building in North Dakota in terms of stories. [Bergane] Hangeul (the Korean alphabet) has 19 consonants. [Poo Sung] 19 is the smallest prime whose reversal is composite. [Gupta] The smallest prime using/ending with a composite digit. [Murthy] The smallest number (coincidentally prime) with an additive persistence of 2. [Gupta] The only prime that is equal to the difference of two prime cubes. [Gupta] The decimal expansion of 19^{19} begins with the digits 19. This is not true for p^{p}, where p is any other prime less than 19,000,000,019. [Caldwell] "19" is the term used to describe a worthless hand in the game of cribbage. [Cary] The smallest invertible prime. The VicePresident of the United States rates a 19gun salute. [Dobb] Sigmund Freud was 19 years older than Carl Jung. (2^191)/(21) and (2^19+1)/(2+1) are both primes. [Dobb] Earth's mass (5.9736 * 10^{24}) and volume (1.083*10^{12}) are both multiples of 19. Earth's volume is in fact a multiple of 19^{2}. The first prime number presenting and meaning the same value within the "western" world and the "arabic" is the number 19. All other recognizable prime numbers are with the combination of a 1 and 9. [ThaCoDa] The speed limit (in miles per hour) on the private roads of the Cambourne development near Cambridge, England. [Croll] The 19th Fibonacci number is the smallest F(P) which is composite where P is itself prime. [Rupinski] The only number or prime for which there is no palindrome with a digit sum n and beginning with n. [Murthy] If p, q, r, s are consecutive prime numbers such that p > q > r > s > 19, then floor((p * q)/(r * s)) = 1. [Capelle] 19 is the 1  9th prime number. [Caldwell] 19 people had been hanged by the time the Salem witch hysteria died down in 1692. [La Haye] 19 is the smallest twodigit number such that 19^19+191 is prime. [Opao] The sum of 19 consecutive Fibonacci numbers starting from the 19th Fibonacci number is prime. [Opao] There are exactly 19 primes beginning with the digit 2 among primes smaller than one thousand. [Capelle] The smallest prime formed from distinct nonprime digits. [Silva] 19^19  2 is prime. Note that it starts with the digits 19. [Patterson] 19^{2} = 361 and 3*6+1 = 19. [Madras] 19 is the largest prime factor of 1444  the smallest perfect square to end in three 4's. Note that 4 is the only nonzero digit that can repeat at the end of a perfect square, and the most consecutive 4's that can appear in such a place is three. [Litman] The smallest twodigit prime with a prime ASCII code: 3139 (in base 16) = 12601. [Necula] 19 divides the concatenation of the integers from 19 down to 1. [De Geest] Professor Barabási and his team have found that the World Wide Web on average has 19 clicks of separation between webpages. [McAlee] Article 19 of the Universal Declaration of Human Rights: "Everyone has the right to the freedom of opinion and expression; this right includes freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers." [McAlee] 2^19  19 is prime. [Schlesinger] The smallest prime p such that p^p is pandigital. [Patterson] 19 is the smallest super2 number (curiously prime), i.e., an integer n such that 2n^2 contains 2 consecutive 2s in its decimal representation. [De Geest] The largest value of n less than a thousand, such that 2^{n}+3^{n}+5^{n}+7^{n} is prime. [Opao] 19 is the smallest prime equal to the product of twin primes plus their arithmetic mean (3*5 + 4 = 19). [Teofilatto] Paul Hardcastle had a hit song called "19." [Wolfe] The second (and last) trip of the USS Absaroka across the Atlantic to European waters ended in New York in February 1919. On December 24, 1941, the Japanese submarine I19 fired two torpedoes at that same ship, which was carrying a cargo of lumber, two miles off Pt. Fermin (San Pedro, California). The ship didn't sink but one sailor was killed by falling lumber. [Haga] 19 is the smallest prime of the form 3p + 2q, where p and q are twin primes. [Teofilatto] 19 is the smallest prime with a digital root of 1. [McAlee] Any number that is divisible by 19 will have this property: multiply the last digit by 2, then add that number to the remaining digits and the resulting number will be divisible by 19. E.g., 625632 is divisible by 19 because all of following results are divisible by 19:(62563 + 4 = 62567); (6256 + 14 = 6270); (627 + 0 = 627); (62 + 14 = 76); (7 + 12 = 19); (1 + 18 = 19). [Beedle] 19 is the only prime p less than 30 that does not divide 30, where p + 30 is composite. [Axoy] 19 is the only known number for which both (10^n1)/9 and (10^n+1)/11 are primes. 19 + 18 + ... + 1 + 0 = 190. [Brand] phi(19)  (19) = 1 + 9. 19 is the only prime with this property. [Firoozbakht] The sum of the first powers of 9 and 10 and the difference between the second powers of 9 and 10. [Gardner] Football legend Johnny Unitas wore jersey number 19. [Hutchins] Consider a square made of four rigid rods, hinged at the ends. How many rods of the same type must be added to make the square rigid in the plane? The answer is 19, which makes a total of 23 rods (also prime). [McCranie] Here is the mathematical code to determine if a number is divisible by 19. Multiply everything in front of the last digit by nine and subtract the last digit. If you get zero, nineteen, or a multiple of nineteen, the number will be divisible by 19. For example 57. Five times nine minus seven equals 38. Since 19 divides evenly into 38, it divides evenly into 57. Next example 114. Eleven times nine minus four equals 95. Since 19 divides evenly into 95, it divides evenly into 114. [Young] 19 is the smallest prime mentioned a prime number of times in the KJV Bible. [Opao] The smallest multidigit number (coincidentally prime) that does not form a palindrome when added to its reversal. [Capelle] The only twodigit prime n such that n!/reversal(n)+1 and n!/reversal(n)1 are both prime. [Patterson] The prime rate published in The Wall Street Journal was 19.00 on October 5, 1981. This remains the highest primenumbered prime rate since that time. [Goelz] Not counting Panno's resignation (1. c4 resigns), Bobby Fischer won 19 consecutive games at the World Championship Interzonal tournament and Candidates matches in 197071. [McCranie] The Fractran algorithm (John Horton Conway's primeproducing machine) is an interesting but terribly inefficient way to generate prime numbers. It requires 19 steps to compute the first prime, 2. D. H. Lehmer's electromechanical number sieve used 19 bicycle chains. [Bell] The first verse of the Qur'an (known as "Basmalah") consists of 19 Arabic letters. [Yuksel] The following are primes: 19, 109, 1009, 10009. No other digit can replace the 9 and yield four primes. [This is the first entry listed as a "Prime Curio" in the book NUMBERS: Fun & Facts by J. Newton Friend; Charles Scribner's Sons, New York (1954); Library of Congress Catalog No. 548690, p. 45.] Farideh Firoozbakht improved the Papadimitriou's conjecture and proposed that every prime number p greater than or equal to 19 can be written as p = 2q + 3r, where q and r are odd primes. [Capelle] An unistable polyhedron is stable on only one face. The simplest such polyhedron known requires 19 faces. Whether unistability is possible with fewer faces is an unsolved problem. [McCranie] The first prime p such that p^2 is the reversal of a prime (163). [Silva] 19 terms are required in the GregoryLeibniz series, i.e., 4(1  1/3 + 1/5  1/7 + 1/9  ...), for the first appearance of "3.1" in the decimal expansion of . In chess positions with a king and pawn versus a king in which pawn promotion can be forced, at most 19 moves are required to promote the pawn (with best play by both sides). [McCranie] The smallest prime which is the sum of two semiprimes in two different ways. [Post] 19^0 + 19^1 + ... + 19^18 (19 terms) is prime. [Caldwell] The largest prime that is palindromic in Roman numerals alphabetically is XIX (19). [Beedassy] The smallest titanic hexagonalcongruent prime has 19 ones on each of its six sides. Therefore each side of this hexagon is a repunit prime. C19A became the largest iceberg in the world after the previous largest iceberg cracked into two different pieces. (It is the size of Brunei.) [Junie] 19 is the "age of majority" adopted under federal jurisdiction in two US states, viz., Nebraska, Alabama. [Beedassy] "Let me tell you how it will be. There's one for you, 19 for me." Lyrics by George Harrison from the song "Taxman" by The Beatles. [Post] The sum of all singledigit semiprimes. Insert two 0's between its digits and you will have the sum of the cubes of those semiprimes. [Silva] The index p of the largest known Mersenne prime M_{p} = 2^{p}  1 having an associated perfect number M_{p}*2^{p  1} that is short of a prime by 1. [Beedassy] 19 = 1*5 + 3*3 + 5*1. [Poo Sung] The largest natural number n for which the sum of digits is not smaller than n/2. [Capelle] The number of topologically distinct planar configurations without discontinuities that are possible using six matches. [Beedassy] Both numbers reversal(19!  1) and reversal(19! + 1) are primes. 19 is the largest known prime with this property. [Firoozbakht] The number of characters in www.primecurios.com is prime. [Matheny] 19 is the only known prime of the form n^n  8. The next prime in this form (if it exists) will have more than 34000 digits. [Firoozbakht] The MathScience Innovation Center in Richmond, Virginia, is governed by a 19member board consisting of a superintendent and school board member from each consortium division and several atlarge members. 19 is the smallest prime which is the sum of three discrete composites (4 + 6 + 9). [Post] Some positions (e.g., "superflip") on the original Rubik's Cube cannot be solved in 19 or less face turns. Only known prime of the form p*prime(p)^p + 1, where p is prime. [Firoozbakht] Each individual batch of Maker's Mark Whisky is less than 19 barrels. [Leonard] The number of emirps that can be shown on a 12hour digital clock. [Fellows] There are 19 visible diamond patterns on the surface of a fully formed rhombic triacontahedron when structured using a series of phiratio pyramids. An example being Roger von Oech's Ball of Whacks. [Trace] The last 19 digits of 17^18 is prime. [Gupta] The number of letters in the anagrammatic title "A Superb Mosaic  Dare it !" that fittingly qualifies the "PRIME CURIOS DATABASE" with a poetic touch. [Beedassy] Appears to be the largest of the set of primes that cannot be represented as the sum of four distinct primes {2,3,5,7,11,13,19}. [Post] If the congruences proposed by Sierpinski are solved, a 19digit number k is obtained as their smallest solution. [Slate] There are exactly 19 primes between 2^{5}1 and 2^{7}1. Is this the only example of a prime number of primes between two consecutive Mersenne primes? In the card game cribbage, players may refer colloquially to a hand scoring zero points as having a score of 19. [Homewood] The Longest Single Arch Steel Span Bridge in the Western Hemisphere is located northeast of Fayetteville, WV, on US Highway 19 across the New River Gorge. (11, 13, 17, 19) is the first prime quadruple (p, q, r, s) such that s divides pqr+1. [Loungrides] NINETEEN: God's Signature in Nature and Scripture by Edip Yuksel is described as a comprehensive demonstration of the prophetic miracle. Pandigital palindromic primes start as 19digit numbers. [Beedassy] Thomas Jefferson argued that "Every constitution, then, and every law, naturally expires at the end of NINETEEN years. If it be enforced longer, it is an act of force, and not of right." Thomas Jefferson to James Madison, 1789. [Yuksel] Take the nine pairs (a,b) with a+b=19; take the sum a*b+19 for all these nine pairs; ALL the sums are primes. 19 is the largest prime that will do this. [Bergot] The only known prime p of form 4*q+7, where q and 4*p+7 are prime. [Loungrides] Alpha Natural Resources (ANR) forecast coal use to grow more than competing fuels in 19 of the 26 years between 2010 and 2035. 19 = 10011 in base two and 10011 is triangular in base ten. (2^2*3^3*19^19) + 1 is prime. [Honaker]
(There are 46 curios for this number that have not yet been approved by an editor.)
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