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 A209515 #9 Oct 06 2015 21:53:16 %S A209515 598491,181445643,56515446141,17769569448759,5607670578249789, %T A209515 1772313933013227273,560493388203596285283,177302245070678360735145, %U A209515 56092636774113844825575603,17746700710940389030443863763 %N A209515 Number of (n+1) X 7 0..2 arrays with the number of clockwise edge increases in every 2 X 2 subblock equal to the number of counterclockwise edge increases. %C A209515 Column 6 of A209517. %H A209515 R. H. Hardin, <a href="/A209515/b209515.txt">Table of n, a(n) for n = 1..210</a> %e A209515 Some solutions for n=4: %e A209515 ..2..2..1..1..1..1..0....0..2..0..1..2..2..1....2..0..1..2..1..0..1 %e A209515 ..0..0..2..1..1..1..0....1..0..2..0..1..2..1....1..2..0..1..0..1..1 %e A209515 ..2..2..2..1..1..1..0....2..1..0..2..0..1..0....1..1..2..0..1..1..1 %e A209515 ..1..1..1..2..1..1..1....2..1..1..0..2..0..0....0..0..1..2..0..0..0 %e A209515 ..2..1..1..2..1..2..1....1..0..0..0..0..2..2....1..0..0..1..2..2..0 %K A209515 nonn %O A209515 1,1 %A A209515 _R. H. Hardin_, Mar 09 2012