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 A200449 #7 Jul 22 2025 15:49:35 %S A200449 26,142,728,3788,19802,103726,548204,2916664,15576706,83481240, %T A200449 448758338,2418733790,13066215896,70726653732,383520053994, %U A200449 2082953525918,11328873637896,61694898371006,336368349457684,1835858710497508 %N A200449 Number of -3..3 arrays x(0..n+1) of n+2 elements with zero sum and nonzero first and second differences. %C A200449 Column 3 of A200454 %H A200449 R. H. Hardin, <a href="/A200449/b200449.txt">Table of n, a(n) for n = 1..200</a> %e A200449 Some solutions for n=3 %e A200449 .-3...-3....0....2...-1....3....0....0....3....1....1...-2...-3...-1....3...-3 %e A200449 ..2....0....2....3....1...-3....3....1...-1...-3...-2...-3....2...-2...-3...-2 %e A200449 .-3...-1...-3...-3...-2...-2....0....3....1....3...-1....0....3....1...-1....2 %e A200449 ..3....3...-1...-2....2....2...-2...-3...-3....1....3....2....1...-1....3....1 %e A200449 ..1....1....2....0....0....0...-1...-1....0...-2...-1....3...-3....3...-2....2 %K A200449 nonn %O A200449 1,1 %A A200449 _R. H. Hardin_ Nov 18 2011