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 A243643 #29 Aug 12 2022 20:17:39 %S A243643 0,0,0,6,62,362,1266,3692,8904,19376,38144,70574,122478,203722,324554, %T A243643 500868,749128,1094204,1560240,2183562,2998598,4055502,5402450, %U A243643 7107528,9233488,11870016,15100040,19037586,23787678,29495558,36290898,44354248,53846392,64985376 %N A243643 Number of non-degenerate parallelograms in an n X n permutation array. %C A243643 A non-degenerate parallelogram has positive area. %H A243643 Christopher N. Swanson, Randy Ho, Bill Correll, Jr., <a href="/A243643/b243643.txt">Table of n, a(n) for n = 1..1000</a> %H A243643 Mathematics Stack Exchange, <a href="http://math.stackexchange.com/questions/709461/counting-non-degenerate-parallelograms-in-permutation-arrays">Counting non-degenerate parallelograms in permutation arrays</a> %K A243643 nonn %O A243643 1,4 %A A243643 _Christopher N. Swanson_, Randy Ho, _Bill Correll, Jr._, Jun 08 2014