A100361 Numbers k such that 2^k - k + 1 is prime.

0, 1, 2, 4, 6, 16, 18, 54, 58, 100, 120, 504, 1302, 3234, 14748, 16102, 22782, 34656, 64764, 70866, 194940, 274074, 313344, 331416, 354640

Offset: 1

Author

Labos Elemer, Nov 19 2004

Keywords

• nonn
• hard
• more

Comments

a(21) > 150000. - Giovanni Resta, Mar 18 2014

a(26) > 5*10^5. - Robert Price, Oct 13 2014

Crossrefs

Cf. A001580, A052007, A048744, A100357-A100359, A061421.

Programs

Maple

A100361:=n->`if`(isprime(2^n-n+1), n, NULL): seq(A100361(n), n=0..10^3); # Wesley Ivan Hurt, Oct 13 2014

Mathematica

{ta={{0}}, tb={{0}}};Do[g=n;s=2^n-n+1; If[PrimeQ[s], Print[n];ta=Append[ta, n]; tb=Append[tb, s]], {n, 1, 10000}];{ta, tb, g}

PARI

is(n)=ispseudoprime(2^n-n+1) \\ Charles R Greathouse IV, Feb 20 2017

Extensions

a(15)-a(20) from Giovanni Resta, Mar 18 2014

a(21)-a(25) from Robert Price, Oct 13 2014