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 A199831 #7 Jul 22 2025 13:24:23 %S A199831 140,1820,21364,273728,3579520,47040968,622300326,8281149188, %T A199831 110718596524,1486040082748,20010711643976,270217094416868, %U A199831 3657780168834780,49618552941019396,674346504318284036 %N A199831 Number of -7..7 arrays x(0..n+1) of n+2 elements with zero sum and no two neighbors summing to zero. %C A199831 Column 7 of A199832 %H A199831 R. H. Hardin, <a href="/A199831/b199831.txt">Table of n, a(n) for n = 1..200</a> %e A199831 Some solutions for n=3 %e A199831 .-7...-1....5....0...-6....0....2...-3...-4....5...-7....4...-5...-6....0...-3 %e A199831 .-1....2...-7...-2...-5...-4....1...-7....3....0....6...-6....4....1....1...-3 %e A199831 .-4...-3...-6....6....3....6....3....0...-1...-7....2...-5....0...-3...-2....5 %e A199831 ..7...-3....2....0....7...-5....1....3....5....5....0....3...-2....2....3....7 %e A199831 ..5....5....6...-4....1....3...-7....7...-3...-3...-1....4....3....6...-2...-6 %K A199831 nonn %O A199831 1,1 %A A199831 _R. H. Hardin_ Nov 11 2011