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 A224662 #6 Jul 23 2025 05:17:00 %S A224662 6,24,128,222,500,956,1876,3538,6622,12200,22274,40302,72418,129332, %T A224662 229780,406378,715800,1256248,2197512,3832510,6665570,11563364, %U A224662 20012598 %N A224662 Number of n X n 0..5 matrices with each 2X2 subblock idempotent. %C A224662 Column 5 of A224665 %F A224662 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 A224662 Some solutions for n=3 %e A224662 ..0..0..0....1..1..4....1..0..5....1..1..3....1..0..2....1..0..2....1..0..0 %e A224662 ..0..0..0....0..0..0....1..0..1....0..0..0....1..0..1....1..0..1....1..0..1 %e A224662 ..2..1..1....0..0..0....0..0..1....5..1..1....2..0..1....4..0..1....3..0..1 %K A224662 nonn %O A224662 1,1 %A A224662 _R. H. Hardin_ Apr 14 2013