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 A195521 #7 Jul 22 2025 12:45:00 %S A195521 1,1,15,1695,2563933,46387885537,10665939121760907, %T A195521 31749804821289929290261 %N A195521 Number of lower triangles of an n X n -7..7 array with all row and column sums zero. %C A195521 Column 7 of A195522 %e A195521 Some solutions for n=4 %e A195521 ..0........0........0........0........0........0........0........0 %e A195521 .-1.1......2-2.....-4.4......7-7.....-2.2.....-3.3......3-3......6-6 %e A195521 ..3-1-2....1.4-5....3-5.2...-4.0.4...-4.1.3....3-3.0....2.1-3...-2.5-3 %e A195521 .-2.0.2.0.-3-2.5.0..1.1-2.0.-3.7-4.0..6-3-3.0..0.0.0.0.-5.2.3.0.-4.1.3.0 %K A195521 nonn %O A195521 1,3 %A A195521 _R. H. Hardin_ Sep 20 2011