%I #6 Mar 21 2015 06:11:14

%S 1,2,8,2,12,864,4,10,8,72,18,38,2144,178,472,974,2200,8128,4580,822,

%T 3600,4100

%N Least k such that Mersenne-prime(n)*2^k+1 is prime (A000668(n)*2^k+1).

%t mexp = {the list in A000043}; f[n_] := Block[{k = 1, mp = 2^mexp[[n]] - 1}, While[ !PrimeQ[mp*2^k + 1] && k < 10000, k++ ]; If[k == 10000, 0, k]]; Do[ Print[ f[n]], {n, 22}] (* _Robert G. Wilson v_, Sep 13 2004 *)

%Y Cf. A098472.

%K nonn

%O 1,2

%A _Pierre CAMI_, Sep 09 2004

%E a(18)-a(22) from _Robert G. Wilson v_, Sep 13 2004