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 A201955 #8 Dec 29 2023 23:06:33 %S A201955 7,231,1587,17903,194633,2232183,25952953,305979795,3640250461, %T A201955 43624267941,525774918227,6366440653727,77388201173481, %U A201955 943784967491137,11542145313593503,141498452574240619,1738344524754583621 %N A201955 Number of zero-sum n X 2 -3..3 arrays with every element unequal to at most two horizontal and vertical neighbors. %C A201955 Column 2 of A201958. %H A201955 R. H. Hardin, <a href="/A201955/b201955.txt">Table of n, a(n) for n = 1..68</a> %e A201955 Some solutions for n=4 %e A201955 ..2..3...-3.-3...-2.-3...-2..3...-2..1....2.-3....2.-3....2..0...-3.-1....1.-2 %e A201955 ..0..0....2..2....1..1....0..0...-2..0....1..1....3.-3....0.-1....3..0....0..0 %e A201955 .-2.-2...-1.-1....2..2....1..1....2..0....0..0....3..0....0.-1....3..0....0..0 %e A201955 .-2..1....3..1....0.-1...-1.-2....2.-1...-1..0...-2..0....3.-3...-2..0....3.-2 %Y A201955 Cf. A201958. %K A201955 nonn %O A201955 1,1 %A A201955 _R. H. Hardin_, Dec 06 2011