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 A224664 #8 Jul 23 2025 05:17:19 %S A224664 8,32,200,318,700,1292,2476,4570,8406,15256,27498,49198,87530,154940, %T A224664 273084,479466,838944,1463400,2545472,4416198,7643450,13199732, %U A224664 22747870,39126778,67176430 %N A224664 Number of n X n 0..7 matrices with each 2X2 subblock idempotent. %C A224664 Column 7 of A224665 %F A224664 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 %F A224664 Empirical g.f.: 8*x -2*x^2 *(-16 -4*x +249*x^2 -516*x^3 +238*x^4 +241*x^5 -199*x^6 -31*x^7 +35*x^8) /(x-1)^3 /(x^2+x-1)^3 . - _R. J. Mathar_, Nov 09 2018 %e A224664 Some solutions for n=3 %e A224664 ..1..0..0....1..0..4....1..1..6....1..1..5....1..0..0....1..0..6....1..1..2 %e A224664 ..1..0..0....0..0..1....0..0..0....0..0..0....1..0..1....1..0..1....0..0..0 %e A224664 ..4..0..0....0..0..1....0..1..1....0..0..1....1..0..1....2..0..1....7..1..1 %K A224664 nonn %O A224664 1,1 %A A224664 _R. H. Hardin_ Apr 14 2013