A271392 Integers k such that 3*k!!! + 1 is prime where k!!! is A007661(k).

2, 4, 5, 8, 9, 15, 16, 23, 27, 32, 34, 35, 38, 40, 46, 54, 57, 83, 87, 97, 162, 165, 223, 235, 282, 488, 503, 575, 673, 823, 857, 885, 965, 1112, 1401, 2288, 2569, 2788, 3133, 3539, 4070, 4654, 5020, 5613, 6720, 7773, 11256, 18023, 22196

Offset: 1

Author

Altug Alkan, Apr 06 2016

Keywords

• nonn
• more

Comments

Corresponding primes are 7, 13, 31, 241, 487, 87481, 174721, 289027201, 21427701121, ...

Examples

			4 is a term because 3*4!!! + 1 = 13 is prime.
		

Crossrefs

Cf. A007661, A037083, A084438, A217647, A215779, A271396.

Programs

PARI

is(k) = ispseudoprime(3*prod(i=0, (k-2)\3, k-3*i) + 1); \\ Jinyuan Wang, Jun 09 2021

Extensions

a(47) from Jinyuan Wang, Jun 09 2021

a(48)-a(49) from Michael S. Branicky, Aug 10 2024