A036980 Number of (2n) X (2n) symmetric matrices each of whose rows is a permutation of 1..(2n).
1, 2, 96, 328320, 440952422400
Offset: 0
Formula
a(n) = A035483(n) * (2n)!
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.