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 A200548 #7 Jul 22 2025 15:51:51 %S A200548 30,200,1184,7254,43698,266812,1639804,10152636,63132188,394016210, %T A200548 2466471522,15481097890,97396742734,614019893832,3878005568152, %U A200548 24532092598782,155413031752230,985836563404470,6260856742508844 %N A200548 Number of -3..3 arrays x(0..n+1) of n+2 elements with zero sum and nonzero second differences. %C A200548 Column 3 of A200553 %H A200548 R. H. Hardin, <a href="/A200548/b200548.txt">Table of n, a(n) for n = 1..200</a> %e A200548 Some solutions for n=3 %e A200548 ..2....0....3...-2...-3...-1....0...-1....0....3....1...-2...-1...-1....3....0 %e A200548 .-3....1...-1....3....3....0...-1...-1....3...-2...-2....1....2....3...-3...-1 %e A200548 .-1...-1...-1...-3...-1...-1...-1....2....1....1....3...-3....3...-2....3....1 %e A200548 ..3...-2....1....2...-2....1....0....2...-2...-3...-3....2...-3...-3...-1...-2 %e A200548 .-1....2...-2....0....3....1....2...-2...-2....1....1....2...-1....3...-2....2 %K A200548 nonn %O A200548 1,1 %A A200548 _R. H. Hardin_ Nov 19 2011