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 A224663 #6 Jul 23 2025 05:17:07 %S A224663 7,28,162,268,596,1118,2166,4038,7488,13686,24818,44640,79796,141848, %T A224663 250966,442168,776152,1357850,2368298,4119186 %N A224663 Number of n X n 0..6 matrices with each 2X2 subblock idempotent. %C A224663 Column 6 of A224665 %F A224663 Empirical: a(n) = 6*a(n-1) -12*a(n-2) +5*a(n-3) +12*a(n-4) -12*a(n-5) -3*a(n-6) +6*a(n-7) -a(n-9) for n>10 %e A224663 Some solutions for n=3 %e A224663 ..1..1..2....1..1..6....1..1..4....0..0..0....0..1..0....1..1..0....1..0..3 %e A224663 ..0..0..0....0..0..0....0..0..0....0..0..0....0..1..0....0..0..0....1..0..1 %e A224663 ..2..1..1....3..1..1....6..1..1....4..1..1....0..1..0....0..0..1....2..0..1 %K A224663 nonn %O A224663 1,1 %A A224663 _R. H. Hardin_ Apr 14 2013