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181 is the 9th palindromic prime number. Note that 9 divides 18 and 81, whose sum of digits are both 9. There are 181 digits in 111!. [De Geest] The 181st prime is congruent to 1 (mod 181). [Haga] The prime value of x in the equation x^{2} = 2^{(3 * 5)}  7. 181 * 10^{181} + (10^{181}  1) is prime. [Luhn] The sum of the first 181 primes minus 181 is prime. [Gevisier] The sum of the digits of the first 23 primes (2, ..., 83). [Trotter] The 181digit palindromic number made up of all 7's except for the center nut being 181 (7777...7718177...77777) is a palindromic prime with a palindromic prime decimal length. [Fougeron] The first occurrence of two consecutive primes which are both nontrivial (more than one digit) palindromes: 181, 191. [Murthy] The smallest palindromic prime that remains prime through four iterations of the function f(x) = 2x + 5. [Russo] The smaller of the first occurrence of two successive primes using no prime digits (181, 191). [Murthy] The surface area of a pair Boeing 757 wings in square meters. 181 pennies currently minted in the U.S. weigh within a penny of a pound. 181 is the smallest odd prime (and fifth in all) exponent of 2 dissecting the interval between successive primes, i.e., 2^181 + 165 are both prime with no intervening primes. [King] 181 = 9^{2} + 10^{2}, i.e., the sum of two consecutive squares. [Mizuki] No ship of the United States Navy has ever been named USS Haynes. A fictitious USS Haynes (DE181) was the setting for the surface half of the movie The Enemy Below; her part was played by USS Whitehurst (DE634). [Haga] The smaller prime in the first multidigit "Gridgeman pair." A Gridgeman pair is two palindromic primes, which differ only in that their middle digits are x and x + 1 respectively. These are named in honor of Norman T. Gridgeman (19121995) who conjectured that there are an infinite number of primes in this form. [King] The smallest palindromic prime number whose sum of digits is composite. Note that 181 is also the smallest such that at least one of the digits is composite. [Capelle] 181^2 = 105^3  104^3, i.e., a solution to the Diophantine equation z^2 = x^3  y^3. [Mizuki] It is conjectured that there is always a prime between x^{a} and y^{b} for all integers x, y, a, b > 1, except for the following ten pairs: (2^{3},3^{2}), (5^{2},3^{3}), (2^{5},6^{2}), (11^{2},5^{3}), (3^{7},13^{3}), (5^{5},56^{2}), (181^{2},2^{15}), (43^{3},282^{2}), (46^{3},312^{2}), and (22434^{2},55^{5}). [Redmond and Sun] The smallest palindromic prime resulting from the sum of three consecutive emirps (37, 71, 73). [Silva] The smallest prime which is a ddigit palindrome base 10 as well as a ddigit palindrome for some base b different from 10. [Post] Every natural number greater than 181 can be written as sum of cubes of the first two primes. [Capelle] 181 candidates were nominated for the Nobel Peace Prize the year Al Gore won it. [Francis] The smallest prime decimal Goedelization of a theorem from propositional calculus, symbolizing "A is logically equivalent to A." [Post] Only number n such that prime(n) = 6n + 1. [Firoozbakht] The sum of strobogrammatic numbers less than or equal to 181 equals 666. (see OEIS A230833) Can you find another strobogrammatic prime of the form (5n^2+5n+2)/2? [Honaker] "Cosmos: A Spacetime Odyssey" premiered in 181 countries. There are at least 181 Las Bolas Grandes ('The Great Stone Balls' in Spanish) of Costa Rico that survive whole. [Lothrop] The complex vitamin B12 molecule contains a total of 181 atoms. [Newmark] List all the whole numbers less than 1000, that is 0  999. The number of whole numbers in the list containing the digit 0 is 181. [Green] 181 is a palindromic Pythagorean prime, equal to the sum of the squares of 10 and 9. [Green]
(There are 12 curios for this number that have not yet been approved by an editor.)
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