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 A195643 #7 Jul 22 2025 12:45:29 %S A195643 1,1,3,19,391,25532,5539434,4116290300,10699674783969, %T A195643 98827025484631957,3284291571314714878300 %N A195643 Number of lower triangles of an n X n 0..7 array with all row sums equal to the length of the row and all column sums equal to the length of the column. %C A195643 Column 7 of A194644 %e A195643 Some solutions for n=7 %e A195643 ..1..............1..............1..............1..............1 %e A195643 ..1.1............0.2............2.0............2.0............2.0 %e A195643 ..0.3.0..........0.3.0..........3.0.0..........2.1.0..........2.1.0 %e A195643 ..4.0.0.0........2.1.1.0........0.2.2.0........1.3.0.0........2.2.0.0 %e A195643 ..0.2.2.0.1......2.0.1.1.1......1.1.2.0.1......1.2.2.0.0......0.1.0.3.1 %e A195643 ..1.0.1.0.2.2....2.0.2.0.2.0....0.3.0.1.2.0....0.0.2.4.0.0....0.1.4.0.1.0 %e A195643 ..0.0.2.4.0.0.1..0.0.1.3.0.2.1..0.0.1.3.0.2.1..0.0.1.0.3.2.1..0.1.1.1.1.2.1 %K A195643 nonn %O A195643 1,3 %A A195643 _R. H. Hardin_ Sep 21 2011