2,4

Table of n, a(n) for n=2..75.

a[n_] := Block[{f=(2*n-1)!!, m=0}, While[! PrimeQ[f - 2^m], m++]; m]; a /@ Range[2, 75] (* Giovanni Resta, Feb 14 2013 *)

Cf. A212281, A212282, A212321, A212636, A212637.

Sequence in context: A253187 A139755 A213366 * A255507 A195052 A104637

Adjacent sequences: A212645 A212646 A212647 * A212649 A212650 A212651

nonn

Vladimir Shevelev, Feb 14 2013

a(8)-a(75) from Giovanni Resta, Feb 14 2013

approved