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 A217269 #8 Apr 23 2021 09:39:23 %S A217269 4,441,33856,2572816,194881600,14755689729,1117092569476, %T A217269 84567501131481,6401965110822961,484642857129680209, %U A217269 36688499987102073289,2777397165745966328049,210254833741528740686404 %N A217269 Number of n X 4 arrays of occupancy after each element moves to some horizontal or vertical neighbor. %C A217269 Column 4 of A217273. %H A217269 R. H. Hardin, <a href="/A217269/b217269.txt">Table of n, a(n) for n = 1..38</a> %F A217269 Empirical: a(n) = 102*a(n-1) -2037*a(n-2) +2098*a(n-3) +111987*a(n-4) -459828*a(n-5) -54016*a(n-6) +1828299*a(n-7) -2079066*a(n-8) +455875*a(n-9) +352710*a(n-10) -165978*a(n-11) +15218*a(n-12) +1308*a(n-13) -111*a(n-14) +a(n-15). %e A217269 Some solutions for n=3 %e A217269 ..0..1..0..0....1..1..0..2....1..3..1..1....1..0..0..1....1..2..2..1 %e A217269 ..1..1..3..2....1..1..2..1....0..2..1..0....1..2..0..3....2..0..0..1 %e A217269 ..2..0..1..1....2..0..1..0....0..1..2..0....0..3..0..1....2..0..0..1 %Y A217269 Cf. A217273. %K A217269 nonn %O A217269 1,1 %A A217269 _R. H. Hardin_ Sep 29 2012