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 A207731 #7 Jul 22 2025 20:44:27 %S A207731 9,81,189,441,2163,10609,33063,103041,418263,1697809,5875227,20331081, %T A207731 77333859,294156801,1057136187,3799119769,14123193995,52502848225, %U A207731 191262879795,696752470089,2569117858827,9473043664561,34677617171731 %N A207731 Number of 4Xn 0..1 arrays avoiding 0 0 0 and 0 1 0 horizontally and 0 1 1 and 1 0 1 vertically. %C A207731 Row 4 of A207729 %H A207731 R. H. Hardin, <a href="/A207731/b207731.txt">Table of n, a(n) for n = 1..210</a> %F A207731 Empirical: a(n) = a(n-1) +12*a(n-3) +98*a(n-4) +12*a(n-5) +34*a(n-6) -230*a(n-7) -1980*a(n-8) -508*a(n-9) +340*a(n-10) +840*a(n-11) +9800*a(n-12) +3000*a(n-13) +2000*a(n-15) -10000*a(n-16) %e A207731 Some solutions for n=4 %e A207731 ..1..0..1..1....1..1..1..0....0..0..1..1....1..1..0..1....1..1..0..0 %e A207731 ..1..1..1..1....0..1..1..1....0..1..1..1....1..1..0..1....1..1..0..1 %e A207731 ..0..0..1..1....0..1..1..0....1..0..1..1....1..0..0..1....1..1..1..0 %e A207731 ..0..0..1..1....1..1..0..0....0..0..1..1....1..0..0..1....1..1..0..0 %K A207731 nonn %O A207731 1,1 %A A207731 _R. H. Hardin_ Feb 19 2012