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 A220998 #6 Jul 23 2025 01:36:43 %S A220998 8,306,11017,394580,14113081,504635391,18042682111,645084293748, %T A220998 23063745428252,824598809224499,29481898439700635,1054066854447577743, %U A220998 37686070858394633616,1347390750744270331311,48173285030655948141067 %N A220998 Number of nX3 arrays of occupancy after each element stays put or moves to some horizontal or vertical neighbor. %C A220998 Column 3 of A221001 %H A220998 R. H. Hardin, <a href="/A220998/b220998.txt">Table of n, a(n) for n = 1..29</a> %F A220998 Empirical: a(n) = 45*a(n-1) -327*a(n-2) -189*a(n-3) +2183*a(n-4) -1362*a(n-5) +976*a(n-6) +10221*a(n-7) +3837*a(n-8) -432*a(n-9) -11*a(n-10) %e A220998 Some solutions for n=3 %e A220998 ..0..3..0....0..4..0....0..3..1....0..2..2....1..2..0....0..3..0....1..2..2 %e A220998 ..3..2..1....1..1..0....3..0..0....0..1..1....2..2..0....2..1..1....1..0..1 %e A220998 ..0..0..0....1..0..2....1..0..1....0..2..1....0..0..2....2..0..0....2..0..0 %K A220998 nonn %O A220998 1,1 %A A220998 _R. H. Hardin_ Dec 28 2012