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 A207726 #7 Jul 22 2025 20:43:59 %S A207726 15,225,611,2163,8575,27931,88243,288813,926949,2927115,9278885, %T A207726 29390445,92717065,292337359,921806095,2904391209,9147369231, %U A207726 28808166663,90713456051,285607327515,899181685831,2830809676285,8911643119525 %N A207726 Number of nX5 0..1 arrays avoiding 0 0 0 and 0 1 0 horizontally and 0 1 1 and 1 0 1 vertically. %C A207726 Column 5 of A207729 %H A207726 R. H. Hardin, <a href="/A207726/b207726.txt">Table of n, a(n) for n = 1..210</a> %F A207726 Empirical: a(n) = 4*a(n-1) -3*a(n-2) +10*a(n-3) -27*a(n-4) -6*a(n-5) -15*a(n-6) +51*a(n-7) +41*a(n-8) +31*a(n-9) -51*a(n-10) -29*a(n-11) -27*a(n-12) +15*a(n-13) +6*a(n-14) +3*a(n-15) -4*a(n-16) +a(n-17) +a(n-19) %e A207726 Some solutions for n=4 %e A207726 ..1..0..1..1..1....1..0..1..1..1....1..0..1..1..0....0..0..1..1..0 %e A207726 ..1..0..1..1..0....0..1..1..1..1....1..0..1..1..1....1..0..1..1..0 %e A207726 ..1..0..1..1..0....0..0..1..1..1....0..0..1..1..0....0..1..1..1..1 %e A207726 ..0..1..1..0..1....1..0..1..1..1....0..1..1..0..0....0..0..1..1..0 %K A207726 nonn %O A207726 1,1 %A A207726 _R. H. Hardin_ Feb 19 2012