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

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..47.

Example

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

Prog

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

Crossrefs

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

Sequence in context: A080403 A280050 A360772 * A195364 A279793 A305076

Adjacent sequences: A271389 A271390 A271391 * A271393 A271394 A271395

Keyword

nonn,more

Author

Altug Alkan, Apr 06 2016

Extensions

a(47) from Jinyuan Wang, Jun 09 2021

Status

approved