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 A199826 #7 Jul 22 2025 13:23:47 %S A199826 10,40,114,426,1650,6126,23206,88636,337866,1295566,4992364,19269156, %T A199826 74529210,288954786,1122363984,4366362420,17011617426,66365823648, %U A199826 259213619826,1013542247970,3966939195402,15540399135516,60929935280508 %N A199826 Number of -2..2 arrays x(0..n+1) of n+2 elements with zero sum and no two neighbors summing to zero. %C A199826 Column 2 of A199832 %H A199826 R. H. Hardin, <a href="/A199826/b199826.txt">Table of n, a(n) for n = 1..200</a> %e A199826 Some solutions for n=3 %e A199826 ..0....0...-1....0...-1....1...-1...-1....1....1...-1...-2....0...-2....1....1 %e A199826 ..1...-1...-2...-2....2....2....0...-2....0....2...-2....1....2...-2....1...-2 %e A199826 .-2...-1....0....0....0....1...-1....1....1....0....1....0...-1....1....0...-1 %e A199826 ..1....2....2....2....1...-2....2....1...-2...-1....2....2...-1....2...-2....2 %e A199826 ..0....0....1....0...-2...-2....0....1....0...-2....0...-1....0....1....0....0 %K A199826 nonn %O A199826 1,1 %A A199826 _R. H. Hardin_ Nov 11 2011