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 A199825 #8 Jul 22 2025 13:23:40 %S A199825 2,4,4,10,22,34,66,138,250,472,944,1806,3450,6772,13172,25478,49794, %T A199825 97348,189772,371246,727506,1424586,2793034,5483342,10766950,21154424, %U A199825 41599648,81840866,161080918,317230034,625030514,1231964394,2429323642 %N A199825 Number of -1..1 arrays x(0..n+1) of n+2 elements with zero sum and no two neighbors summing to zero. %C A199825 Column 1 of A199832 %H A199825 R. H. Hardin, <a href="/A199825/b199825.txt">Table of n, a(n) for n = 1..200</a> %e A199825 All solutions for n=3 %e A199825 .-1....0....0....1 %e A199825 .-1....1...-1....1 %e A199825 ..0....0....0....0 %e A199825 ..1...-1....1...-1 %e A199825 ..1....0....0...-1 %K A199825 nonn %O A199825 1,1 %A A199825 _R. H. Hardin_ Nov 11 2011