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 A200549 #7 Jul 22 2025 15:51:58 %S A200549 52,446,3396,26850,211374,1689732,13587804,109957140,893510530, %T A200549 7288331916,59637096784,489325754576,4024444316206,33167657580268, %U A200549 273853057747366,2264784856966600,18757225819498566,155553439876468586 %N A200549 Number of -4..4 arrays x(0..n+1) of n+2 elements with zero sum and nonzero second differences. %C A200549 Column 4 of A200553 %H A200549 R. H. Hardin, <a href="/A200549/b200549.txt">Table of n, a(n) for n = 1..200</a> %e A200549 Some solutions for n=3 %e A200549 ..0....0...-3...-3...-1...-4...-1....1...-2...-3....0...-1...-1...-2....1...-3 %e A200549 ..2...-1....3....2....1...-4....3....2...-3....0....3....1....3...-3...-2....1 %e A200549 .-4....2...-4....1...-2....1....0...-4....4...-3....4...-1...-2...-3....2....3 %e A200549 ..0...-4....3....1...-1....3....2....4...-1....3...-3...-1...-1....4....1....3 %e A200549 ..2....3....1...-1....3....4...-4...-3....2....3...-4....2....1....4...-2...-4 %K A200549 nonn %O A200549 1,1 %A A200549 _R. H. Hardin_ Nov 19 2011