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 A200051 #8 Jul 22 2025 15:39:15 %S A200051 1,4,10,26,68,178,472,1276,3462,9496,26024,71956,198740,552814, %T A200051 1535556,4290252,11968194,33553214,93917400,264020106,741024426, %U A200051 2087799972,5872999754,16577458520,46720454112,132081262316,372843051320 %N A200051 Number of -2..2 arrays x(0..n-1) of n elements with zero sum and elements alternately strictly increasing and strictly decreasing. %C A200051 Column 2 of A200057 %H A200051 R. H. Hardin, <a href="/A200051/b200051.txt">Table of n, a(n) for n = 1..200</a> %e A200051 Some solutions for n=6 %e A200051 .-1...-1....0....2....0....0....0....0....0...-2....0....0....1...-1...-2...-2 %e A200051 ..1...-2...-1....1....1...-1....1....1...-1....1....2...-2....2....1....1....1 %e A200051 ..0....2....0....2...-2....2...-2...-1....1...-1...-2....0...-2....0....0...-1 %e A200051 ..2...-2...-1...-2....0...-2....1....0....0....1....0...-1....2....1....1....1 %e A200051 .-2....2....2...-1...-1....1...-2...-2....1....0...-1....2...-2...-1...-2...-1 %e A200051 ..0....1....0...-2....2....0....2....2...-1....1....1....1...-1....0....2....2 %K A200051 nonn %O A200051 1,2 %A A200051 _R. H. Hardin_ Nov 13 2011