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 A035482 #13 May 05 2023 09:56:37 %S A035482 1,1,2,6,96,720,328320,31449600,440952422400,444733651353600, %T A035482 471835793808949248000,10070314878246926155776000, %U A035482 1058410183156945383046388908032000,614972203951464612786852376432607232000 %N A035482 Number of n X n symmetric matrices each of whose rows is a permutation of 1..n. %C A035482 The even and odd subsequences are A036980, A036981. %F A035482 a(n) = A035481(n) * n!. [From _Max Alekseyev_, Apr 23 2010] %e A035482 a(3) = 6 because the first row is arbitrary (say, 213) and the rest is then determined. By symmetry the second row has to be 132 or 123 but in order for the third row/column to work it has to be 132. %Y A035482 Cf. A000438, A035481, A000315, A002860, A003090, A040082. %K A035482 more,nonn %O A035482 0,3 %A A035482 _Joshua Zucker_ and Joe Keane %E A035482 a(10)-a(13) (using A035481) from _Alois P. Heinz_, May 05 2023