A124887 - OEIS

%I #6 Dec 15 2017 17:37:06

%S 1,3,5,3,3,5,11,5,13,3,3,5,5,17,7,7,19,25,15,9,61,49,7,5,17,5,13,3,9,

%T 29,33,9,73,13,39,5,53,39,7,3,7,5,45,5,19,19,73,31,141,83,29,49,25,11,

%U 21,53,37,49,39,13,41,9,47,25,61,139,33,11,133,39,93,49,93,41,7,15,67,121

%N Least positive k such that n * 2^n + k is prime.

%D J. Earls, Red Zen, Lulu Press, NY, 2006, p. 135.

%t lpk[n_]:=Module[{c=n*2^n,k=1},While[!PrimeQ[c+k],k=k+2];k]; Array[lpk,80] (* _Harvey P. Dale_, Oct 08 2017 *)

%K easy,nonn

%O 1,2

%A _Jason Earls_, May 19 2007