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 A210926 #7 Jul 22 2025 22:37:33 %S A210926 0,1,4,95,9220,3055073,3000338892,8812917082915,76878364475257062, %T A210926 1995945343880703817038,154116672749530867319434810 %N A210926 Number of n X n 0..3 symmetric matrices with every element equal to one, two or three horizontal and vertical neighbors, and new values 0..3 introduced in lower triangle row major order. %e A210926 Some solutions for n=4 %e A210926 ..0..0..1..0....0..0..1..1....0..0..0..1....0..0..0..0....0..0..1..1 %e A210926 ..0..0..1..0....0..0..1..1....0..1..1..1....0..1..1..0....0..0..1..0 %e A210926 ..1..1..2..2....1..1..1..0....0..1..1..0....0..1..1..0....1..1..1..0 %e A210926 ..0..0..2..2....1..1..0..0....1..1..0..0....0..0..0..0....1..0..0..0 %K A210926 nonn %O A210926 1,3 %A A210926 _R. H. Hardin_ Mar 29 2012