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 A201798 #7 Jul 22 2025 16:20:41 %S A201798 19,455,4057,48335,562961,7099021,90062519,1168520339,15269686011, %T A201798 201396758073,2670595602167,35597100656221,476317522683397, %U A201798 6395415423401799,86112911010980123,1162374111689802707 %N A201798 Number of zero-sum nX3 -2..2 arrays with every element unequal to at most two horizontal and vertical neighbors. %C A201798 Column 3 of A201803 %H A201798 R. H. Hardin, <a href="/A201798/b201798.txt">Table of n, a(n) for n = 1..40</a> %e A201798 Some solutions for n=4 %e A201798 .-2.-2.-2....1.-1..1....1..1.-2....0..1..1...-1..0..0....1..1.-2....1.-2..2 %e A201798 ..2..2..2....0.-1..2...-2.-2..2....2..2..2....1..1..1....1..1.-2...-2.-2..2 %e A201798 .-1.-1.-1....0.-1..2....2.-2..2...-2.-2.-2....0..1..1...-1..1..1....2..2..2 %e A201798 ..2.-1..2...-2.-1..0....2.-2..0...-1.-1..0....0.-2.-2...-1.-1..1...-2.-2.-1 %K A201798 nonn %O A201798 1,1 %A A201798 _R. H. Hardin_ Dec 05 2011