A212637 Minimal m>=0 such that (2*n-1)!! + 2^m is prime.

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

Offset: 1

Author

Vladimir Shevelev, Feb 14 2013

Keywords

• nonn

Crossrefs

Cf. A212281, A212282, A212321, A212636.

Programs

Maple

a:= proc(n) local m;
      for m from 0 while not isprime(doublefactorial(2*n-1)+2^m)
      do od; m
    end:
seq(a(n), n=1..70);  # Alois P. Heinz, Feb 18 2013

Mathematica

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

Extensions

a(9)-a(70) from Giovanni Resta, Feb 15 2013