A271392 - OEIS

%I #23 Aug 10 2024 09:29:17

%S 2,4,5,8,9,15,16,23,27,32,34,35,38,40,46,54,57,83,87,97,162,165,223,

%T 235,282,488,503,575,673,823,857,885,965,1112,1401,2288,2569,2788,

%U 3133,3539,4070,4654,5020,5613,6720,7773,11256,18023,22196

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

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

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

%o (PARI) is(k) = ispseudoprime(3*prod(i=0, (k-2)\3, k-3*i) + 1); \\ _Jinyuan Wang_, Jun 09 2021

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

%K nonn,more

%O 1,1

%A _Altug Alkan_, Apr 06 2016

%E a(47) from _Jinyuan Wang_, Jun 09 2021

%E a(48)-a(49) from _Michael S. Branicky_, Aug 10 2024