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 A206886 #7 Jul 22 2025 19:46:43 %S A206886 21,441,5357,59812,607043,5963040,57268342,544455870,5145953202, %T A206886 48496979643,456336864550,4290529415423,40323106384871, %U A206886 378881102825949,3559611742043731,33440802573235066,314150208927203377 %N A206886 Number of nX5 0..1 arrays avoiding 0 1 0 horizontally and 1 0 0 vertically. %C A206886 Column 5 of A206889 %H A206886 R. H. Hardin, <a href="/A206886/b206886.txt">Table of n, a(n) for n = 1..210</a> %F A206886 Empirical: a(n) = 19*a(n-1) -53*a(n-2) -919*a(n-3) +5094*a(n-4) +17034*a(n-5) -146605*a(n-6) -135493*a(n-7) +2291102*a(n-8) -55688*a(n-9) -22745288*a(n-10) +11388816*a(n-11) +153841613*a(n-12) -119040421*a(n-13) -734469299*a(n-14) +698124793*a(n-15) +2516801724*a(n-16) -2731404740*a(n-17) -6212206591*a(n-18) +7532624063*a(n-19) +10946419938*a(n-20) -14922586530*a(n-21) -13420309714*a(n-22) +21251997154*a(n-23) +10802691232*a(n-24) -21497939840*a(n-25) -4872687712*a(n-26) +15092347688*a(n-27) +350777984*a(n-28) -7105176368*a(n-29) +864704896*a(n-30) +2144653264*a(n-31) -475489632*a(n-32) -393937600*a(n-33) +113200032*a(n-34) +41328672*a(n-35) -13403968*a(n-36) -2255616*a(n-37) +739584*a(n-38) +51712*a(n-39) -14336*a(n-40) %e A206886 Some solutions for n=4 %e A206886 ..1..0..1..1..0....0..0..0..1..1....1..0..1..1..1....1..1..1..1..1 %e A206886 ..1..1..1..0..0....1..1..1..0..1....0..1..1..0..1....0..1..1..1..1 %e A206886 ..1..1..0..1..1....1..0..1..1..0....1..1..0..1..1....1..1..1..1..1 %e A206886 ..0..0..1..1..1....1..1..0..0..1....1..1..1..0..1....0..1..1..1..1 %K A206886 nonn %O A206886 1,1 %A A206886 _R. H. Hardin_ Feb 13 2012