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 A213986 #6 Jul 22 2025 23:05:46 %S A213986 3,72,8168,3510112,5018010431 %N A213986 Number of n X n 0..4 matrices whose square is also a 0..4 matrix. %C A213986 Column 4 of A213990 %e A213986 Some solutions for n=3 %e A213986 ..0..4..1....0..4..4....0..4..4....2..0..0....1..0..2....0..3..2....2..2..0 %e A213986 ..0..0..0....0..0..0....1..0..0....0..2..2....0..2..0....0..1..0....0..0..2 %e A213986 ..0..1..0....0..0..0....0..0..0....0..0..0....0..0..1....0..0..0....0..0..0 %K A213986 nonn %O A213986 1,1 %A A213986 _R. H. Hardin_ Jun 30 2012