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If n is greater than 15, then there is at least one number between n and 2n which is the product of three different primes. [Sierpinski] The number of trees with 15 vertices is prime. The smallest multidigit integer I such that 4*I+1 and 4*I1 are both primes. [Russo] There are exactly 15 palindromic primes of length three. [Patterson] 15 is the smallest number which is product of two distinct odd primes. [Capelle] !15  1 is prime. Note that !15 represents subfactorial 15. [Gupta] 15 is the only number m such that m = ((m)!_{2}). [Firoozbakht] 15 is the smallest emirpime. [Post] 15 is the (1+5)th Lucky Number. [Post] (F_{0}^{15} + F_{1}^{15} + F_{2}^{15} + F_{3}^{15} + F_{4}^{15}) and (F_{0}^{15} + F_{1}^{15} + F_{2}^{15} + F_{3}^{15} + F_{4}^{15} + 6) are sexy primes. Note that the first five Fermat numbers are all prime. [Wesolowski] 15!14!+ ... +3!2!+1! is prime. [Silva] The only known natural number n > 0 such that the sum of the five known Fermat primes raised to the power n is prime. Curiously, it is the product of the first two Fermat primes. [Capelle] (15) = 1 + 5. [Kumar] The number of supersingular primes, i.e., primes that divide the order of the Monster group (an algebraic construction with 2^{46} * 3^{20} * 5^{9} * 7^{6} * 11^{2} * 13^{3} * 17 * 19 * 23 * 29 * 31 * 41 * 47 * 59 * 71 elements). [Capelle] 15 is closer to a prime than any multiple of below it. [Honaker]
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