A279904 Primes of the form n^2*2^n - 1.

71, 6271, 20971519999, 3696558092582911, 71248353479884799, 36607563614276605181951, 66626319770601443076406771711, 46716685589841799771959773105092594214371327, 3855174423960385883723562689229267550261846474751

Offset: 1

Author

Juri-Stepan Gerasimov, Jan 17 2017

Keywords

• nonn

Examples

			a(1) = 3^2*2^3 - 1 = 71 is prime where 3 = A058781(1).
a(2) = 7^2*2^7 - 1 = 6271 is prime where 7 = A058781(2).
		

Crossrefs

Cf. A058781.

Programs

Magma

[a: n in [1..45] | IsPrime(a) where a is n^2*2^n-1];

Mathematica

Select[Table[n^2 2^n - 1, {n, 0, 150}], PrimeQ] (* Vincenzo Librandi, Jan 20 2017 *)

PARI

select(ispseudoprime, apply(n->n^2*2^n - 1, [1..200])) \\ Charles R Greathouse IV, Jan 20 2017

Formula

a(n) = A000040(A058781(n)).