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 A199904 #7 Jun 02 2025 05:25:12 %S A199904 1,4,24,72,256,1312,5206,21208,97668,422052,1819620,8158144,36110122, %T A199904 159422584,712790438,3182921756,14206099012,63688577860,285783359204, %U A199904 1282956672032,5770687400200,25983122754016,117074268243396 %N A199904 Number of -3..3 arrays x(0..n-1) of n elements with zero sum, and adjacent elements not equal modulo three (with -1 modulo 3 = 2). %C A199904 Column 3 of A199909 %H A199904 R. H. Hardin, <a href="/A199904/b199904.txt">Table of n, a(n) for n = 1..200</a> %e A199904 Some solutions for n=6 %e A199904 .-2....2...-1...-1....1...-2...-1...-2...-3...-3....2....2....2....3...-3...-1 %e A199904 ..3...-3....1....0...-3...-1....1....2....2...-1....0....1...-3...-1....2...-2 %e A199904 .-2....1....2...-2....1....0...-1....1....1....3....2...-1....1...-3...-3...-3 %e A199904 ..2....3....3....0....3....2....0...-3....0...-1...-3...-3...-3...-2....1....2 %e A199904 .-3...-2...-2....1...-2....1....1....2...-2....0...-1....1....1....2....2....3 %e A199904 ..2...-1...-3....2....0....0....0....0....2....2....0....0....2....1....1....1 %K A199904 nonn %O A199904 1,2 %A A199904 _R. H. Hardin_ Nov 11 2011