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 A195520 #7 Jul 22 2025 12:44:53 %S A195520 1,1,13,1105,1089411,11131321791,1252997799222737, %T A195520 1582560262323178069903 %N A195520 Number of lower triangles of an n X n -6..6 array with all row and column sums zero. %C A195520 Column 6 of A195522 %e A195520 Some solutions for n=4 %e A195520 ..0........0........0........0........0........0........0........0 %e A195520 ..0.0......0.0......0.0.....-3.3.....-5.5.....-2.2......5-5.....-5.5 %e A195520 ..4.0-4...-4.4.0....3-2-1...-3.3.0...-1-3.4....4.0-4...-6.4.2....3-4.1 %e A195520 .-4.0.4.0..4-4.0.0.-3.2.1.0..6-6.0.0..6-2-4.0.-2-2.4.0..1.1-2.0..2-1-1.0 %K A195520 nonn %O A195520 1,3 %A A195520 _R. H. Hardin_ Sep 20 2011