This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A161738 #10 Jul 22 2025 06:42:29
%S A161738 1,1,3,15,35,315,693,9009,19305,328185,692835,14549535,30421755,
%T A161738 760543875,1579591125,45808142625,94670161425,3124115327025,
%U A161738 6432002143875,237984079323375,488493636505875,20028239096740875
%N A161738 Sequence related to the column sums of the BG2 matrix.
%H A161738 G. C. Greubel, <a href="/A161738/b161738.txt">Table of n, a(n) for n = 1..667</a>
%F A161738 a(n) = product((2*n-3-2*k), k=0..floor(n/2-1)).
%F A161738 numer(a(n+2)/a(n+1)) = A005408(n) for n=>0.
%F A161738 denom(a(n+2)/a(n+1)) = A093178(n) for n=>0.
%t A161738 Table[Product[(2*n - 3 - 2*k), {k, 0, Floor[n/2 - 1]}], {n, 1, 50}] (* _G. C. Greubel_, Sep 26 2018 *)
%o A161738 (PARI) for(n=1,50, print1(prod(k=0,floor(n/2 -1), 2*n-2*k-3), ", ")) \\ _G. C. Greubel_, Sep 26 2018
%o A161738 (Magma) [1] cat [(&*[2*n-2*k-3:k in [0..Floor(n/2 -1)]]): n in [2..50]]; // _G. C. Greubel_, Sep 26 2018
%Y A161738 Cf. A161736, A005408 and A093178.
%K A161738 easy,nonn
%O A161738 1,3
%A A161738 _Johannes W. Meijer_, Jun 18 2009