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 A213985 #6 Jul 22 2025 23:05:39 %S A213985 2,36,2546,604639,421195466,801373175814 %N A213985 Number of n X n 0..3 matrices whose square is also a 0..3 matrix. %C A213985 Column 3 of A213990 %e A213985 Some solutions for n=3 %e A213985 ..1..0..0....0..2..1....1..2..1....0..3..0....0..0..2....0..1..3....0..1..0 %e A213985 ..0..0..3....0..0..0....0..0..0....0..1..1....0..1..1....0..0..1....0..1..0 %e A213985 ..0..0..1....0..0..1....1..0..0....0..2..0....0..1..1....0..0..0....0..1..1 %K A213985 nonn %O A213985 1,1 %A A213985 _R. H. Hardin_ Jun 30 2012