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A212321 Minimal m >= 1 such that floor((2*n-1)!!/m) + 2 is prime.

%I A212321 #20 Oct 28 2020 11:10:42
%S A212321 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 A212321 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 A212321 21,17,47,37,3,7,67,23,23,25,45,81,5,39,145,71,21,41
%N A212321 Minimal m >= 1 such that floor((2*n-1)!!/m) + 2 is prime.
%H A212321 Alois P. Heinz, <a href="/A212321/b212321.txt">Table of n, a(n) for n = 1..500</a>
%p A212321 a:= proc(n) local m;
%p A212321       for m while not isprime(iquo(doublefactorial(2*n-1), m)+2)
%p A212321       do od; m
%p A212321     end:
%p A212321 seq(a(n), n=1..50);  # _Alois P. Heinz_, Feb 18 2013
%t A212321 a[n_] := Module[{m}, For[m = 1, True, m++, If[PrimeQ[Floor[(2n-1)!!/m]+2], Return[m]]]];
%t A212321 Array[a, 100] (* _Jean-François Alcover_, Oct 28 2020 *)
%Y A212321 Cf. A212281, A212282.
%K A212321 nonn
%O A212321 1,6
%A A212321 _Vladimir Shevelev_, Feb 14 2013
%E A212321 More terms from _Alois P. Heinz_, Feb 18 2013