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 A221407 #5 Jul 23 2025 01:53:15 %S A221407 8,328,12668,492102,18852560,722442370,27665242848,1058237377670 %N A221407 Number of nX6 arrays of occupancy after each element stays put or moves to some horizontal or vertical neighbor, with every occupancy equal to zero or two. %C A221407 Column 6 of A221408 %e A221407 Some solutions for n=3 %e A221407 ..0..0..2..0..2..2....0..0..2..2..0..2....2..2..0..2..0..2....2..0..0..0..2..0 %e A221407 ..2..0..0..2..0..0....2..0..2..0..0..2....2..0..0..2..0..0....2..2..2..2..2..0 %e A221407 ..2..0..2..2..0..2....0..2..2..0..0..2....0..2..2..0..2..0....0..0..2..0..0..2 %K A221407 nonn %O A221407 1,1 %A A221407 _R. H. Hardin_ Jan 15 2013