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 A221261 #5 Jun 02 2025 08:14:02 %S A221261 0,4096,5822,1250753956,278802326676,1080371161000000, %T A221261 720107530988047980,1273696206975009956961,1220346471047321694829098 %N A221261 Number of 7Xn arrays of occupancy after each element moves to some horizontal or antidiagonal neighbor, with no occupancy greater than 2. %C A221261 Row 7 of A221255 %e A221261 Some solutions for n=3 %e A221261 ..1..2..0....0..2..2....0..2..0....1..2..0....1..2..0....0..2..0....1..2..0 %e A221261 ..1..2..0....0..2..0....1..2..0....0..2..0....0..2..1....1..2..0....0..2..0 %e A221261 ..0..2..2....0..2..1....2..2..0....1..2..1....0..2..1....1..2..1....1..2..1 %e A221261 ..0..2..0....0..2..0....0..2..0....0..2..0....0..2..0....1..2..1....0..2..0 %e A221261 ..0..2..1....2..2..0....1..2..1....2..2..0....1..2..2....0..2..1....1..2..0 %e A221261 ..0..2..2....0..2..1....1..2..1....0..2..1....0..2..1....0..2..0....1..2..1 %e A221261 ..0..2..0....0..2..1....0..2..0....0..2..1....0..2..0....1..2..0....1..2..0 %K A221261 nonn %O A221261 1,2 %A A221261 _R. H. Hardin_ Jan 06 2013