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 A195641 #9 May 17 2020 01:41:03 %S A195641 1,1,3,19,391,25532,5536654,4102276124,10576325574496, %T A195641 96132191056438654,3112190512707436846248,361888107612909923618319047, %U A195641 152218183506656720143679173709254,233008581159686014846657554273887832751 %N A195641 Number of lower triangles of an n X n 0..5 array with all row sums equal to the length of the row and all column sums equal to the length of the column. %e A195641 Some solutions for n=5: %e A195641 ..1..........1..........1..........1..........1..........1..........1 %e A195641 ..0.2........1.1........0.2........0.2........2.0........1.1........0.2 %e A195641 ..0.1.2......0.1.2......0.2.1......2.1.0......2.1.0......0.1.2......1.0.2 %e A195641 ..3.1.0.0....2.1.1.0....4.0.0.0....1.0.2.1....0.3.1.0....2.2.0.0....2.1.0.1 %e A195641 ..1.0.1.2.1..1.1.0.2.1..0.0.2.2.1..1.1.1.1.1..0.0.2.2.1..1.0.1.2.1..1.1.1.1.1 %Y A195641 Column 5 of A195644. %K A195641 nonn %O A195641 1,3 %A A195641 _R. H. Hardin_, Sep 21 2011 %E A195641 a(12)-a(14) from _Andrew Howroyd_, May 16 2020