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