A110931 Numbers k such that 2*k^k - 1 is prime.

2, 3, 357, 1400, 205731, 296598

Offset: 1

Author

Ray G. Opao, Sep 25 2005

Keywords

• more
• nonn
• hard

Comments

a(5) > 4000. - Ray G. Opao, Oct 23 2014

a(5) > 101000. - Serge Batalov, Apr 13 2018

Examples

			3 is in the sequence since 2*3^3 - 1 = 53 is prime.
		

Crossrefs

Numbers k such that b*k^k - b + 1 is prime: this sequence (b=2), A301521 (b=4), A302123 (b=6).

Cf. A110932, A062207, A108318.

Programs

Magma

[n: n in [0..500] | IsPrime(2*n^n-1)]; // Vincenzo Librandi, Nov 01 2014

Mathematica

Select[Range[1000], PrimeQ[2*#^# - 1] &] (* Vaclav Kotesovec, Oct 31 2014 *)

PARI

for(n=1,2000,1;if(isprime(2*n^n-1),print(n))) \\ Ray G. Opao, Oct 23 2014

Extensions

a(5-6) from Ryan Propper, Jul 24-28 2022