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 A221271 #7 Jul 23 2025 01:47:41 %S A221271 0,16,0,596,0,24366,0,1001855,0,41171316,0,1691327788,0,69470653170,0, %T A221271 2853337539621,0,117191717993760,0,4813242705044572,0, %U A221271 197686734633818238,0,8119268451165592095,0 %N A221271 Number of nX3 arrays of occupancy after each element moves to some king-move neighbor, with every occupancy equal to zero or two. %C A221271 Column 3 of A221273 %e A221271 Some solutions for n=4 %e A221271 ..0..2..0....2..2..0....0..2..0....0..0..2....2..0..2....0..2..2....2..0..0 %e A221271 ..0..2..0....2..0..0....2..2..0....2..2..2....2..2..0....2..2..0....2..0..2 %e A221271 ..2..0..0....2..0..0....0..2..2....0..2..2....2..0..0....0..2..0....2..2..0 %e A221271 ..2..2..2....0..2..2....0..2..0....0..0..0....0..2..0....0..2..0....0..0..2 %K A221271 nonn %O A221271 1,2 %A A221271 _R. H. Hardin_ Jan 08 2013