A089130 - OEIS

%I #25 Oct 14 2024 01:36:24

%S 2,13,61,2521,20161,3113510401,10461394944001,

%T 132626429906095529318154240000001,

%U 30207631531686917818677566034256998753632256000000001

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

%H Vincenzo Librandi, <a href="/A089130/b089130.txt">Table of n, a(n) for n = 1..13</a>

%F a(n) = A139149(A082672(n)). - _Amiram Eldar_, Oct 13 2024

%t Select[Table[(n!+2)/2,{n,0,100}],PrimeQ] (* _Vincenzo Librandi_, Dec 07 2011 *)

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

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

%Y Cf. A082672, A139149.

%K nonn,changed

%O 1,1

%A _Cino Hilliard_, Dec 05 2003