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 A195518 #7 Jul 22 2025 12:44:39 %S A195518 1,1,9,369,121367,286168923,5151383545261,720374496860187931, %T A195518 798423610752730381095001 %N A195518 Number of lower triangles of an n X n -4..4 array with all row and column sums zero. %C A195518 Column 4 of A195522 %e A195518 Some solutions for n=4 %e A195518 ..0........0........0........0........0........0........0........0 %e A195518 ..3-3......4-4......3-3.....-3.3.....-3.3.....-1.1.....-2.2......1-1 %e A195518 .-3.4-1....0.0.0...-3.0.3....2-1-1....2-3.1....0-4.4...-2.1.1....1.0-1 %e A195518 ..0-1.1.0.-4.4.0.0..0.3-3.0..1-2.1.0..1.0-1.0..1.3-4.0..4-3-1.0.-2.1.1.0 %K A195518 nonn %O A195518 1,3 %A A195518 _R. H. Hardin_ Sep 20 2011