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 A213993 #6 Jul 22 2025 23:06:28 %S A213993 6327,120133,604639,3510112,9131098,29365738,56599992,127113628, %T A213993 255379242,499365458,784233528,1531915046,2261261860,3473439982, %U A213993 5267581848,8552671195,11581885709,17881607889,23603815011,34808081571 %N A213993 Number of 4X4 0..n matrices whose square is also a 0..n matrix. %C A213993 Row 4 of A213990 %H A213993 R. H. Hardin, <a href="/A213993/b213993.txt">Table of n, a(n) for n = 1..40</a> %e A213993 Some solutions for n=3 %e A213993 ..0..2..1..0....1..0..2..3....0..1..1..2....0..0..1..0....1..0..0..0 %e A213993 ..0..0..0..0....0..1..1..0....0..1..0..0....0..0..1..2....0..0..1..2 %e A213993 ..0..3..0..0....0..0..0..0....0..0..0..0....1..0..0..0....0..0..1..3 %e A213993 ..1..2..0..0....0..0..0..0....1..1..0..0....1..0..0..0....1..0..0..0 %K A213993 nonn %O A213993 1,1 %A A213993 _R. H. Hardin_ Jun 30 2012