A089130 Primes of the form (k! + 2)/2.

2, 13, 61, 2521, 20161, 3113510401, 10461394944001, 132626429906095529318154240000001, 30207631531686917818677566034256998753632256000000001

Offset: 1

Author

Cino Hilliard, Dec 05 2003

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..13

Crossrefs

Cf. A082672, A139149.

Programs

Magma

[ a: n in [1..50] | IsPrime(a) where a is (Factorial(n)+2) div 2 ];

Mathematica

Select[Table[(n!+2)/2,{n,0,100}],PrimeQ] (* Vincenzo Librandi, Dec 07 2011 *)

PARI

nfactp2d2(n) = { for(x=1,n, y=floor((x!+ 2)/2); if(isprime(y),print1(y",")) ) }

Formula

a(n) = A139149(A082672(n)). - Amiram Eldar, Oct 13 2024