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 A331645 #9 Jan 25 2020 17:55:56 %S A331645 1,3,87,11655,4498191,3611504823,5192498314767,12172382140406295, %T A331645 43436006002867938351,224018914608150321575223, %U A331645 1603777845822934662938327247,15430102163147097295950086754135,194280602846166109497542618768659311,3131120528310366432743101620841328437623 %N A331645 Number of nonnegative integer matrices with n columns and any number of distinct nonzero rows with column sums 3. %H A331645 Andrew Howroyd, <a href="/A331645/b331645.txt">Table of n, a(n) for n = 0..100</a> %e A331645 The a(1) = 3 matrices are: %e A331645 [2] [1] [3] %e A331645 [1] [2] %Y A331645 Row n=3 of A331568. %Y A331645 Cf. A331644. %K A331645 nonn %O A331645 0,2 %A A331645 _Andrew Howroyd_, Jan 23 2020