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 A082672 Numbers n such that (n! + 2)/2 is a prime. 56
 2, 4, 5, 7, 8, 13, 16, 30, 43, 49, 91, 119, 213, 1380, 1637, 2258, 4647, 9701, 12258 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS MATHEMATICA Select[Range[10^2], PrimeQ[(#!+2)/2] &] (* Vladimir Joseph Stephan Orlovsky, Apr 29 2008 *) PROG (PARI) \\ x such that (x!+2)/2 is prime xfactpk(n, k=2) = { for(x=2, n, y = (x!+k)/k; if(isprime(y), print1(x, ", ")) ) } (MAGMA) [ n: n in [1..300] | IsPrime((Factorial(n)+2) div 2) ]; CROSSREFS Cf. A089130. Cf. n!/m-1 is a prime: A002982, A082671, A139056, A139199-A139205; n!/m+1 is a prime: A002981, A082672, A089085, A139061, A139058, A139063, A139065, A151913, A137390, A139071 (1<=m<=10). Sequence in context: A005125 A232832 A272195 * A241808 A247865 A271505 Adjacent sequences:  A082669 A082670 A082671 * A082673 A082674 A082675 KEYWORD easy,nonn AUTHOR Cino Hilliard, May 18 2003 EXTENSIONS More terms from Don Reble, Dec 08 2003 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008 STATUS approved

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