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 A224672 #7 Feb 17 2018 05:31:51 %S A224672 70,123,170,260,381,573,864,1322,2043,3191,5026,7972,12713,20357, %T A224672 32696,52630,84851,136951,221214,357516,578017,934753,1511920,2445750, %U A224672 3956671,6401343,10356854,16756952,27112473,43868001,70978956,114845342 %N A224672 Number of (n+1) X 5 0..2 matrices with each 2 X 2 subblock idempotent. %C A224672 Column 4 of A224676. %H A224672 R. H. Hardin, <a href="/A224672/b224672.txt">Table of n, a(n) for n = 1..210</a> %F A224672 Empirical: a(n) = 4*a(n-1) -5*a(n-2) +a(n-3) +2*a(n-4) -a(n-5) for n>6. %F A224672 Empirical g.f.: x*(70 - 157*x + 28*x^2 + 125*x^3 - 72*x^4 + 3*x^5) / ((1 - x)^3*(1 - x - x^2)). - _Colin Barker_, Feb 17 2018 %e A224672 Some solutions for n=3: %e A224672 ..0..0..1..0..0....1..1..0..1..0....0..1..0..0..0....1..0..0..0..1 %e A224672 ..0..0..1..0..0....0..0..0..1..0....0..1..0..0..0....1..0..0..0..1 %e A224672 ..0..0..1..0..1....0..0..0..1..0....0..1..0..0..0....0..0..0..0..1 %e A224672 ..0..0..1..0..1....0..0..0..1..0....0..1..0..0..1....0..0..0..0..1 %K A224672 nonn %O A224672 1,1 %A A224672 _R. H. Hardin_, Apr 14 2013