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 A202123 #7 Jun 02 2025 07:24:15 %S A202123 15,169,1483,9739,65773,443169,2993875,20229855,136692527,923636217, %T A202123 6241166303,42172597643,284966475203,1925560567969,13011302413343, %U A202123 87919326690553,594084073349817,4014315174232981,27125329889094427 %N A202123 Number of -7..7 arrays of n elements with first, second and third differences also in -7..7. %C A202123 Column 7 of A202124 %H A202123 R. H. Hardin, <a href="/A202123/b202123.txt">Table of n, a(n) for n = 1..210</a> %e A202123 Some solutions for n=5 %e A202123 ..1....0...-2....7....6....0....0...-3....1...-4...-2....6...-6....2...-4....2 %e A202123 ..5....0....1....5...-1....7....1...-2....4...-2....0....3...-2....3...-2...-5 %e A202123 ..7...-2....0....0...-4....7....5....0....3....2....4...-3....0....5...-3...-7 %e A202123 ..7...-1....1...-5...-2....4....5...-1....3....2....5...-7....0....5...-2...-6 %e A202123 ..0...-1....7...-6....0....2....6...-7...-3....4....3...-4....2....0...-3...-2 %K A202123 nonn %O A202123 1,1 %A A202123 _R. H. Hardin_ Dec 11 2011