# 47

This number is a prime.

© Disney/Pixar |

*Tyrannosauras rex* measured up to 47 feet in overall length. [Norris]

It is interesting that the product of 4 consecutive Fibonacci numbers can equal the product of the first 7 primes.

In the Pixar Film *Monsters Inc.*, the scream factory had enjoyed 47 accident-free days at the start of the movie. [Hartley]

There is an abnormally high use of the prime number 47 in episodes of *Star Trek*. For example, in the *Star Trek: Voyager* episode "Infinite Regress," Naomi Wildman reveals that there are 47 sub-orders of the Prime Directive.

The house band for New York City called Black 47 resides on 47th Street.

The British liner *Great Eastern* had a coir fiber launching rope with a circumference of 47 inches.

The AK-47 is the most widespread weapon in the world. [Kalashnikov]

47^{9} can be written as the sum of distinct smaller 9th powers.

The beast number raised to power 47 has sum of digits equal to the beast number. [De Geest]

Auguste Comte coined the word sociology, which appeared for the first time
in a footnote to the 47th lesson of the fourth volume of his *Course of Positive Philosophy*.

47 * 2^{583} + 1, 47 * 2^{1483} + 1 and 47 * 2^{6115} + 1 are the only known primes of the form 47 * 2^{n} + 1. [Ballinger and
Keller]

John Major was 47 years old when he became British Prime Minister in 1990.

The MK-47 was the first and last Soviet calculator with magnetic cards. [Frolov]

47 is self-conscious: 4 + 7 = 11, 7 + 11 = 18, 11 + 18 = 29, and 18 + 29 = 47. It refers to itself. Note that 4, 7 and 47 are Lucas numbers. [Faust]

47 is the first and only prime *p* less than 20000 of the form *p**2^(*p*+1)-1, where *p* is prime. [Luhn]

*Lot 47 Inc.* is a privately owned film company focused on the acquisition and distribution of American independent films as well as high-profile foreign films.

Marine Storm Warnings occur with forecast winds greater than 47 knots. [NOAA]

The KJV Bible was translated by 47 scholars. [English]

"The number 47 may be a flying increment to fill allspace, to fill out the eight triangular facets of the non-allspace-filling vector equilibrium to form the allspace-filling first nuclear cube." (Quoted from section 1238.51 of Synergetics by R. Buckminster Fuller.) [Croll]

47 + 2 equals the reversal of 47 * 2.

There are 47 Pythagorean propositions in Euclid's *Elements*. [Dobb]

It is approximately 47 degrees from the Tropic of Cancer (the greatest distance north that the sun can appear directly overhead) to the Tropic of Capricorn (the greatest distance south that the sun can appear directly overhead). [Obeidin]

Window washer Alcides Moreno survived a 47-story fall from a New York City skyscraper.

*Isaac Asimov's Book of Facts* mentions the "fact" that mosquitoes have 47 teeth. [Patterson]

The gyroelongated pentagonal cupolarotunda has 47 faces. It is the largest prime number of faces a Johnson solid can have. [Hartley]

47 is the largest known number, *n*, such that *n* and *n* + 1 are both Ulam numbers. [McCranie]

The 47 Society is a humorous society at Pomona College in California that propagates the belief that the number 47 is the quintessential random number. Campus lore suggests that Pomona math professor Donald Bentley produced a convincing mathematical proof that 47 was equal to all other integers. (See *www.47.net/47society/*.) [Schuler]

There are an incredible number of references to the number 47 in the TV show *Alias*. [Hunt]

According to Chinese legend, a 16th century official named Wan Hu attempted a flight to the Moon by using two kites fastened to a sedan chair on which he had strapped 47 black powder rockets. 47 servants simultaneously lit the fuses and Wan Hu disappeared in a burst of flame and smoke. A crater on the far side of the Moon (at 9.8°S, 138.8°W) has been named in his honor. [Caldwell]

The surprising formula for primes proposed by J. Minac and C. Willans in 1995 had 47 symbols. This formula, based on Wilson theorem, gives all the primes successively and without repetition, but unfortunately is not very convenient. [Capelle]

47 bones of the "Lucy" skeleton were unearthed in '74.

The modern concert harp typically has 47 strings. [Kamath]

ceil((π + *e*/47)^47) is prime. [Noll]

Mary Mallon, better known as "Typhoid Mary," was a food service worker who infected 47 people with the bacterium *Salmonella enterica typhi*. She was the first "healthy carrier" of typhoid fever in the United States.

The Hadwiger problem asks for the largest number of subcubes (not necessarily different) into which a cube cannot be divided by plane cuts. The answer is 47. [Post]

Mathematician Kevin Hare has proven that any odd perfect number must have at least 47 prime factors, including repetitions.

The smallest prime whose number of perfect partitions is greater than itself. [Beedassy]

In the play *The Five Hysterical Girls Theorem* by Rinne
Groff, renowned number theorist Moses Vazsonyi fears
that he has lost his edge in the intellectually grueling
world of prime number theory at the age of 47.

The first of two consecutive primes whose sum has the form 10^{n}. [Silva]

There are 47 known Mersenne primes (as of 2011). (The 47th discovered is actually the 46th in size).

Can you find the 4 consecutive Fibonacci numbers whose product equals the product of the first 7 prime numbers? Hint: computing the sum of the four consecutive Fibonacci numbers is as easy as 1-2-3.

Henri Emile Benoit Matisse's painting "Le Bateau" hung for 47 days in the Museum of Modern Art, New York City, between October 18 and December 4, 1961, and not a single person noticed it was upside down.

The list of primes begins with a zeroless sequence of 47 digits. [Silva]

In 1958, R. M. Robinson was unable to find a single prime of the form 47 * 2^n + 1.

The sum of the first six primes with distinct end-digits (11+2+3+5+7+19). [Silva]

The largest prime number whose square (2209) can be displayed on a 24-hour digital clock. [Fellows]

Over 47 years after it was first published, "Mastering the Art of French Cooking" by Julia Child finally topped the best-seller list. [Clifford]

The number of triangles in this figure.

The smallest prime of the only pair of two consecutive two-digit primes whose sum of the reversals is prime. [Silva]

The eruption of Mount St. Helens destroyed 47 bridges (May 18, 1980).

A 47-sided polygon is called a tetracontakaiheptagon. [Green]

The forty-seventh Fibonacci and Lucas numbers are both prime and are respectively 2971215073 and 6643838879. Forty-seven represents the largest subscript less than one hundred for which this is true. Among the first one hundred Fibonacci numbers and Lucas numbers, both are prime for the subscripts 4, 5, 7, 11, 13, 17, and 47. [Schiffman]

In 1981, Harry L. Nelson produced a 47-page printout containing the 206,545-digit solution to Archimedes' Cattle Problem. The number was generated from a CRAY-1 supercomputer at the Lawrence Livermore National Laboratory and was published in small type in the Journal of Recreational Mathematics.

47 is the last "totally safe" prime: 47 -> 23 -> 11 -> 5 -> 2 (complete descending sequence of safe primes till 2 is reached). [Wood]

Lavandula is a genus of 47 known species of flowering plants in the mint family, Lamiaceae. [McKenzie]

Klinefelter syndrome (or 47XXY) is a condition in which human males have an extra X chromosome.

Euphemia Lofton Haynes, the first African-American woman to earn a Ph.D. in mathematics, devoted her life to education in the Washington, D.C. area for 47 years.

"47 Ways To Die" is the song heard over the opening and closing credits for the film "The Hit List", 2011, starring Cuba Gooding, Jr. [Green]

The only double-digit prime from which no one prime is obtained by inserting between its digits d d's (where d is any digit). [Loungrides]

The largest double-digit prime ab such that a^a + b^b is prime. [Loungrides]

In the CW show called *The 100*, the captives held at Mount
Weather are referred to as "the 47." [Phillips]

(47, 53, 59, 61) is the only tetrad of successive double-digit primes p < q < r < s such that (p+q) divides r*s+1, i.e., (47+53) divides 59*61+1. [Loungrides]

It's a 47-second elevator ride to the top of One World Trade Center. [Guardian]

The smaller of only two double-digit primes, whose cube, (103823), can be represented as the concatenation of two 3-digit primes. [Loungrides]

Rex Goliath was once the treasured attraction of a Texas circus. People came from far and wide to behold the 47-pound bird, billed as the "World's Largest Rooster."

"47 Meters Down" is a British survival horror film directed by Johannes Roberts. [Barnett]

3 divides 141 a *prime number* of times. Does this ever
happen again in the decimal expansion of π? Note that 3 divides 141592653, but 47197551 is a semiprime.

Prime numbers that end with "47" occur more often than any other 2-digit ending among the first one billion primes. [Gaydos]

The sum of the first 47 positive integers with digits in strictly ascending order is divisible by 47 (2350/47=50). The next and largest such prime is 383 (1848741/383=4827). [Gaydos]

47 (exactly half) of the first 94 prime numbers each has at least one prime twin. [Gaydos]

The largest prime sum of digits among all known Mersenne prime exponents: sod(82589933) = 47. [Harrison]

German doctor Otto Heinrich Warburg was nominated for the Nobel Prize award 47 times over the course of his career. [Hess]

There were 47 people on White Island when a powerful volcanic eruption trapped tourists. [Linkous]

The famous 1728 Chambers' Cyclopedia is made up of 47 sections. [Olry]

47 squares are each adjacent to at least one distinct digit prime number. [Gaydos]

47 is the largest known Lucas prime with a composite index. [Homewood]

"47 Wide Right" was Scott Norwood's missed 47-yard field goal attempt for the Buffalo Bills at the end of Super Bowl XXV. [Williams]

The product of 47 and 4*7 is "perfect" if prime proper divisors are omitted (1+4+14+28+94+188+329+658).