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 A195642 #7 Jul 22 2025 12:45:21 %S A195642 1,1,3,19,391,25532,5539434,4116036800,10694128575819, %T A195642 98630958757213465,3267417937114919996252 %N A195642 Number of lower triangles of an n X n 0..6 array with all row sums equal to the length of the row and all column sums equal to the length of the column. %C A195642 Column 6 of A194644 %e A195642 Some solutions for n=6 %e A195642 ..1............1............1............1............1............1 %e A195642 ..1.1..........1.1..........0.2..........2.0..........0.2..........2.0 %e A195642 ..2.1.0........2.1.0........2.1.0........2.1.0........2.1.0........2.1.0 %e A195642 ..2.0.0.2......1.2.1.0......0.0.3.1......0.2.1.1......0.1.3.0......0.3.1.0 %e A195642 ..0.0.2.1.2....1.0.2.0.2....1.0.1.1.2....0.1.2.2.0....1.0.1.1.2....1.0.2.1.1 %e A195642 ..0.3.2.0.0.1..0.1.1.3.0.1..2.2.0.1.0.1..1.1.1.0.2.1..2.1.0.2.0.1..0.1.1.2.1.1 %K A195642 nonn %O A195642 1,3 %A A195642 _R. H. Hardin_ Sep 21 2011