A058934 Numbers k such that 2*5^k + 1 is prime.

0, 1, 3, 13, 45, 105, 159, 297, 1443, 2977, 3699, 11709, 12357, 43165, 121995

Offset: 1

Author

Labos Elemer, Jan 12 2001

Keywords

• nonn
• more

Comments

a(n) is odd for n > 0. Next term > 17200. - Julián Aguirre, Apr 22 2011

a(16) > 2*10^5. - Robert Price, Mar 14 2015

Examples

			a(3)=13 and 1 + 2*5^13 = 2441406251 is prime.
		

Crossrefs

Cf. A003306 (2*3^n + 1 is prime), A120375 (2*5^n-1 is prime).

Programs

Mathematica

Select[Range[0, 16000], PrimeQ[2*5^#+1]&] (* Julián Aguirre, Apr 22 2011 *)

PARI

is(n)=ispseudoprime(2*5^n+1) \\ Charles R Greathouse IV, Jun 12 2017

Sage

[n for n in range(1500) if is_prime(2*5^n+1)]
# Julián Aguirre, Apr 22 2011

Extensions

Edited by Joerg Arndt, Apr 22 2011

Terms 1443,...,12357 from Julián Aguirre, Apr 22 2011

a(14)-a(15) from Robert Price, Mar 14 2015