A212321 - OEIS

%I #20 Oct 28 2020 11:10:42

%S 1,1,1,1,1,3,9,5,5,3,1,1,7,1,13,11,15,21,23,15,17,5,25,25,7,85,9,25,1,

%T 21,9,13,17,5,49,39,45,1,43,51,145,17,143,85,19,81,63,43,47,77,23,1,3,

%U 21,17,47,37,3,7,67,23,23,25,45,81,5,39,145,71,21,41

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

%H Alois P. Heinz, <a href="/A212321/b212321.txt">Table of n, a(n) for n = 1..500</a>

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

%p       for m while not isprime(iquo(doublefactorial(2*n-1), m)+2)

%p       do od; m

%p     end:

%p seq(a(n), n=1..50);  # _Alois P. Heinz_, Feb 18 2013

%t a[n_] := Module[{m}, For[m = 1, True, m++, If[PrimeQ[Floor[(2n-1)!!/m]+2], Return[m]]]];

%t Array[a, 100] (* _Jean-François Alcover_, Oct 28 2020 *)

%Y Cf. A212281, A212282.

%K nonn

%O 1,6

%A _Vladimir Shevelev_, Feb 14 2013

%E More terms from _Alois P. Heinz_, Feb 18 2013