A049883 Primes in the Jacobsthal sequence (A001045).

3, 5, 11, 43, 683, 2731, 43691, 174763, 2796203, 715827883, 2932031007403, 768614336404564651, 201487636602438195784363, 845100400152152934331135470251, 56713727820156410577229101238628035243

Offset: 1

Author

Judson Neer

Keywords

• nonn

Comments

All terms, except a(2) = 5, are of the form (2^p + 1)/3 - the Wagstaff primes A000979 = {3, 11, 43, 683, 2731, 43691, 174763, ...}.

Indices of prime Jacobsthal numbers are listed in A107036 = {3, 4, 5, 7, 11, 13, 17, 19, 23, 31, 43, 61, ...}.

For n > 1, A107036(n) = A000978(n) (numbers m such that (2^m + 1)/3 is prime). - Alexander Adamchuk, Oct 10 2006

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..23

Crossrefs

Cf. A001045, A000978, A000979, A107036.

Programs

Mathematica

Select[Table[(2^n + (-1)^(n - 1))/3, {n, 200}], PrimeQ] (* Vladimir Joseph Stephan Orlovsky, Mar 29 2011 *)