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 A199893 #7 Jul 22 2025 13:25:51 %S A199893 1,7,25,111,461,2035,8823,39053,172355,767425,3420017,15311495, %T A199893 68665323,308805403,1391091909,6278869703,28381760049,128482271031, %U A199893 582346682067,2642616002605,12004291295381,54583533395613,248409301882015 %N A199893 Number of -3..3 arrays x(0..n-1) of n elements with zero sum, and adjacent elements not both strictly positive and not both strictly negative. %C A199893 Column 3 of A199898 %H A199893 R. H. Hardin, <a href="/A199893/b199893.txt">Table of n, a(n) for n = 1..200</a> %e A199893 Some solutions for n=6 %e A199893 .-2...-2....1...-1....1....0....1....0...-3....1...-3...-1....0...-2....2....1 %e A199893 ..0....3...-2....0...-3....0...-2...-2....3...-2....0....1....3....2...-3...-3 %e A199893 ..2...-2....0....0....2....2....2....1...-1....1....0...-2....0...-1....3....3 %e A199893 ..0....2....1...-1...-2....0...-3....0....0....0....0....3...-2....2...-2...-2 %e A199893 ..3...-2...-2....3....0...-3....3...-1....2....2....0....0....1...-3....1....1 %e A199893 .-3....1....2...-1....2....1...-1....2...-1...-2....3...-1...-2....2...-1....0 %K A199893 nonn %O A199893 1,2 %A A199893 _R. H. Hardin_ Nov 11 2011