A242487 Numbers k such that (2*k)! + k! + 1 is prime.

0, 3, 8, 13, 19, 423, 585, 2746, 2855

Offset: 1

Author

Seiichi Manyama, Mar 22 2018

Keywords

• nonn
• more

Comments

a(10) > 10000. - Michael S. Branicky, May 03 2025

Examples

			0! + 0! + 1 =   3 is prime.
6! + 3! + 1 = 727 is prime.
		

Crossrefs

A300947 gives the primes.

Cf. A002981, A237443.

Programs

Maple

select(k->isprime(factorial(2*k)+factorial(k)+1),[$0..600]); # Muniru A Asiru, May 27 2018

Mathematica

Flatten[{0, Select[Range[100], PrimeQ[(2*#)! + #! + 1] &]}] (* Vaclav Kotesovec, Mar 25 2018 *)

PARI

isok(k) = ispseudoprime((2*k)!+k!+1); \\ Altug Alkan, Mar 22 2018

Extensions

a(8)-a(9) from Michael S. Branicky, Apr 16 2023