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 A200052 #12 Aug 29 2025 08:06:08 %S A200052 1,6,22,78,288,1098,4224,16432,64310,253692,1003374,3992358,15908668, %T A200052 63684848,255153798,1026057576,4127971346,16658240722,67237254862, %U A200052 272092306164,1101134446908,4466186295698,18113540529096,73607652658268,299074725301088,1217290931946978 %N A200052 Number of -3..3 arrays x(0..n-1) of n elements with zero sum and elements alternately strictly increasing and strictly decreasing. %H A200052 R. H. Hardin, <a href="/A200052/b200052.txt">Table of n, a(n) for n = 1..200</a> %e A200052 Some solutions for n=6: %e A200052 .-1...-2....0...-2...-1....1....0...-2...-1....3...-1....1....0....0...-2....1 %e A200052 .-3....0....2....1....1...-2....3....3...-3....0...-3...-2...-1....3....2...-1 %e A200052 ..3...-1...-3...-2...-2....3...-1....1....2....2....3....3....3...-1....0....1 %e A200052 .-1....1....2....2....2...-3....3....3...-1...-3....0...-2....0....1....2...-1 %e A200052 ..2...-1...-3....0...-2....1...-3...-3....2....1....3....2....1...-3...-2....1 %e A200052 ..0....3....2....1....2....0...-2...-2....1...-3...-2...-2...-3....0....0...-1 %Y A200052 Column 3 of A200057. %K A200052 nonn,changed %O A200052 1,2 %A A200052 _R. H. Hardin_, Nov 13 2011