A181636 Primes of form (2^n + 3^n)/13.

61, 4621, 369181, 2414250301, 1282861452271981, 103911691734684541, 102329189594547549657540565413396038701, 28900785585664327723593061693364968422740414514061, 7915715496579381803076374342089862963295414837600820914397695027296168074652778681081092369443226449741

Offset: 1

Author

Michel Lagneau, Nov 18 2010

Keywords

• nonn

Comments

Numbers n such that (2^n + 3^n)/13 is prime are listed in A181628 = {6, 10, 14, 22, 34, 38, 82, 106, 218, 334, 4414 , ...}.

Examples

			4621 is in the sequence because (2^10+ 3^10)/13 = 60073/13 = 4621 is
  prime.
		

Crossrefs

Cf. A181628

Programs

Maple

with(numtheory):for n from 1 to 350 do: x:= (2^n + 3^n)/13:if floor(x)=x and
  type(x,prime)=true then printf(`%d, `, x):else fi:od:

Formula

a(n) = (2^A181628(n) + 3^A181628(n))/13.