A100361 - OEIS

%I #20 Mar 02 2022 10:44:16

%S 0,1,2,4,6,16,18,54,58,100,120,504,1302,3234,14748,16102,22782,34656,

%T 64764,70866,194940,274074,313344,331416,354640

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

%C a(21) > 150000. - _Giovanni Resta_, Mar 18 2014

%C a(26) > 5*10^5. - _Robert Price_, Oct 13 2014

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

%t {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}

%o (PARI) is(n)=ispseudoprime(2^n-n+1) \\ _Charles R Greathouse IV_, Feb 20 2017

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

%K nonn,hard,more

%O 1,3

%A _Labos Elemer_, Nov 19 2004

%E a(15)-a(20) from _Giovanni Resta_, Mar 18 2014

%E a(21)-a(25) from _Robert Price_, Oct 13 2014