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 A221927 #6 Jul 23 2025 02:20:07 %S A221927 13,2197,201378,20246283,2007184132,199492714651,19816266524892, %T A221927 1968651817039048,195572208446932549,19428830291892380296, %U A221927 1930127245301117267451,191745542191155118363255 %N A221927 Number of nX4 arrays of occupancy after each element stays put or moves to some horizontal, diagonal or antidiagonal neighbor, without move-in move-out straight through or left turns. %C A221927 Column 4 of A221929 %H A221927 R. H. Hardin, <a href="/A221927/b221927.txt">Table of n, a(n) for n = 1..49</a> %e A221927 Some solutions for n=3 %e A221927 ..0..3..1..3....0..1..4..0....0..1..0..2....0..0..1..0....0..2..2..0 %e A221927 ..0..0..0..0....0..2..0..0....3..3..0..0....0..2..3..0....0..0..1..1 %e A221927 ..2..0..2..1....0..4..0..1....0..0..2..1....3..0..2..1....0..3..2..1 %K A221927 nonn %O A221927 1,1 %A A221927 _R. H. Hardin_ Feb 01 2013