A271396 Integers k such that 3*k!!! - 1 is prime where k!!! is A007661(k).

0, 1, 2, 4, 5, 6, 7, 8, 10, 17, 25, 28, 31, 37, 38, 39, 46, 47, 49, 55, 67, 82, 85, 94, 98, 115, 120, 129, 167, 214, 216, 267, 293, 580, 732, 857, 993, 1012, 1069, 1308, 1430, 2366, 2974, 4017, 4870, 9034, 9061, 9752, 10657, 13847, 25390

Offset

1,3

Comments

Corresponding primes are 2, 2, 5, 11, 29, 53, 83, 239, 839, 628319, 1825823999, 51123071999, ...

Links

Table of n, a(n) for n=1..51.

Example

4 is a term because 3*4!!! - 1 = 11 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, A271392.

Sequence in context: A190225 A276706 A357018 * A070110 A049095 A324583

Adjacent sequences: A271393 A271394 A271395 * A271397 A271398 A271399

Keyword

nonn,more

Author

Altug Alkan, Apr 06 2016

Extensions

a(46)-a(50) from Jinyuan Wang, Jun 09 2021

a(51) from Michael S. Branicky, Aug 09 2024

Status

approved