A090703 Numbers k such that k*k! + 1 is prime.

1, 2, 3, 4, 5, 7, 12, 19, 23, 45, 58, 149, 151, 197, 682, 879, 1134, 1906, 6616, 10242, 12015

Offset: 1

Author

mohammed bouayoun (bouyao(AT)wanadoo.fr), Jan 15 2004

Keywords

• nonn
• more

Examples

			3*3! + 1 = 19 and 19 is prime, so 3 is a member.
		

Crossrefs

Cf. A049432.

Programs

Mathematica

Do[If[PrimeQ[n*n! + 1], Print[n]], {n, 0, 2000}] (* Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), May 05 2006 *)

PARI

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

Formula

a(n) = A049432(n) - 1.

Extensions

a(17) from Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), May 05 2006

a(18)-a(19) from Jason Earls, Jan 24 2008

a(20) from Seiichi Manyama (by using the data calculated by Donovan Johnson, Dec 18 2009), Mar 22 2018

a(21) from Michael S. Branicky, Jun 11 2025