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 A195640 #9 May 17 2020 01:40:57 %S A195640 1,1,3,19,391,25428,5422820,3868544673,9374373474455, %T A195640 78121590505558308,2262375741577763676620,229653423345084153764141412, %U A195640 82310438395814327559991274396712,104810153877236566878585186368604425875 %N A195640 Number of lower triangles of an n X n 0..4 array with all row sums equal to the length of the row and all column sums equal to the length of the column. %e A195640 Some solutions for n=4: %e A195640 ..1........1........1........1........1........1........1........1 %e A195640 ..2.0......0.2......1.1......0.2......0.2......0.2......1.1......2.0 %e A195640 ..1.0.2....1.0.2....1.0.2....1.0.2....3.0.0....3.0.0....1.0.2....1.0.2 %e A195640 ..0.3.0.1..2.1.0.1..1.2.0.1..2.1.0.1..0.1.2.1..0.1.2.1..1.2.0.1..0.3.0.1 %Y A195640 Column 4 of A195644. %K A195640 nonn %O A195640 1,3 %A A195640 _R. H. Hardin_, Sep 21 2011 %E A195640 a(12)-a(14) from _Andrew Howroyd_, May 16 2020