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 A062156 #7 Feb 03 2021 20:09:46
%S A062156 1,2,13,189,4842,190080,10520010,777018690,73646397720,8696221929360,
%T A062156 1249994376199800,214673857998276600,43377963701592920400,
%U A062156 10180798532673708139200,2745082427076790292091600,842339587833332705318202000,291745985923439508815578224000
%N A062156 Number of n X n matrices over {0,1,2} with all row and column sums equal to 1 or 2.
%D A062156 I. P. Goulden and D. M. Jackson, Combinatorial Enumeration, Wiley, N.Y., 1983,(Problem 3.4.15).
%H A062156 Andrew Howroyd, <a href="/A062156/b062156.txt">Table of n, a(n) for n = 0..100</a>
%e A062156 There are 13 2 X 2 matrices over {0,1,2} with all row and column sums equal to 1 or 2, cf. A062154.
%Y A062156 Main diagonal of A062154.
%Y A062156 Cf. A062155.
%K A062156 easy,nonn
%O A062156 0,2
%A A062156 _Vladeta Jovovic_, Jun 06 2001
%E A062156 Terms a(15) and beyond from _Andrew Howroyd_, Feb 03 2021