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 A036980 #11 May 05 2023 09:26:54 %S A036980 1,2,96,328320,440952422400 %N A036980 Number of (2n) X (2n) symmetric matrices each of whose rows is a permutation of 1..(2n). %F A036980 a(n) = A035483(n) * (2n)! %Y A036980 Cf. A035481, A036981. %K A036980 more,nonn %O A036980 0,2 %A A036980 _Joshua Zucker_ and Joe Keane