A082672 - OEIS

A082672

Numbers n such that (n! + 2)/2 is a prime.

2, 4, 5, 7, 8, 13, 16, 30, 43, 49, 91, 119, 213, 1380, 1637, 2258, 4647, 9701, 12258

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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

KEYWORD

easy,nonn

AUTHOR

EXTENSIONS

More terms from Don Reble, Dec 08 2003

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 03 2008

STATUS

approved