A212637 - OEIS

%I #18 Nov 13 2014 21:36:09

%S 0,1,1,1,1,2,4,3,2,6,1,1,3,1,2,7,5,11,16,2,3,2,4,4,11,6,4,33,1,12,18,

%T 3,20,5,38,17,2,1,18,3,14,26,11,14,63,3,2,13,110,44,34,1,22,44,114,37,

%U 43,39,5,13,12,57,41,12,18,13,9,8,13,52,26,78,37,14

%N Minimal m>=0 such that (2*n-1)!! + 2^m is prime.

%p a:= proc(n) local m;

%p       for m from 0 while not isprime(doublefactorial(2*n-1)+2^m)

%p       do od; m

%p     end:

%p seq(a(n), n=1..70);  # _Alois P. Heinz_, Feb 18 2013

%t a[n_] := Block[{f = (2*n - 1)!!, m = 0}, While[! PrimeQ[f + 2^m], m++]; m]; a/@Range[70] (* _Giovanni Resta_, Feb 15 2013 *)

%Y Cf. A212281, A212282, A212321, A212636.

%K nonn

%O 1,6

%A _Vladimir Shevelev_, Feb 14 2013

%E a(9)-a(70) from _Giovanni Resta_, Feb 15 2013