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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
OFFSET
1,1
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
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