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 A221851 #5 Jul 23 2025 02:17:05 %S A221851 13,3437,465305,67228149,9607602488,1374453486067,196583533871825, %T A221851 28117377558933453 %N A221851 Number of nX4 arrays of occupancy after each element stays put or moves to some horizontal, diagonal or antidiagonal neighbor, without consecutive moves in the same direction. %C A221851 Column 4 of A221852 %e A221851 Some solutions for n=3 %e A221851 ..0..2..1..0....0..2..0..0....0..1..1..0....0..3..0..2....0..4..0..2 %e A221851 ..0..0..3..0....0..1..7..0....1..0..1..4....0..1..0..2....0..0..1..0 %e A221851 ..1..3..2..0....1..0..1..0....0..3..0..1....0..1..1..2....0..3..1..1 %K A221851 nonn %O A221851 1,1 %A A221851 _R. H. Hardin_ Jan 27 2013