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 A213989 #6 Jul 22 2025 23:06:08 %S A213989 3,148,40370,56599992,361204218672 %N A213989 Number of n X n 0..7 matrices whose square is also a 0..7 matrix. %C A213989 Column 7 of A213990 %e A213989 Some.solutions.for.n=3 %e A213989 ..0..1..7....0..5..3....0..2..1....0..1..7....0..2..5....2..0..0....0..7..0 %e A213989 ..0..0..5....0..0..0....0..0..0....0..0..2....0..0..0....0..1..1....0..1..0 %e A213989 ..0..0..0....0..0..0....0..3..2....0..0..0....0..0..1....0..0..1....0..6..0 %K A213989 nonn %O A213989 1,1 %A A213989 _R. H. Hardin_ Jun 30 2012