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 A199892 #8 Jul 22 2025 13:25:43 %S A199892 1,5,15,49,159,533,1783,6027,20437,69665,238191,817083,2809845, %T A199892 9685397,33450675,115736335,401065951,1391807783,4836111471, %U A199892 16823523661,58586196339,204217367081,712482836479,2487770630935,8693076444331 %N A199892 Number of -2..2 arrays x(0..n-1) of n elements with zero sum, and adjacent elements not both strictly positive and not both strictly negative. %C A199892 Column 2 of A199898 %H A199892 R. H. Hardin, <a href="/A199892/b199892.txt">Table of n, a(n) for n = 1..200</a> %e A199892 Some solutions for n=6 %e A199892 .-2....1...-1...-1...-1....1....1...-2...-1....0....2....0....1....0...-2....0 %e A199892 ..0...-1....0....0....2...-1...-1....0....0....1....0...-2....0....2....1....1 %e A199892 ..0....0....0...-1...-1....0....1....2....0...-1....0....0...-2...-2...-1...-1 %e A199892 ..0....2....0....2....2....0...-2...-1....2....0...-2....2....0....1....2....1 %e A199892 ..2...-2....2...-1....0....0....0....1...-2....1....0...-2....1...-1...-1....0 %e A199892 ..0....0...-1....1...-2....0....1....0....1...-1....0....2....0....0....1...-1 %K A199892 nonn %O A199892 1,2 %A A199892 _R. H. Hardin_ Nov 11 2011