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 A200880 #11 Oct 16 2017 10:08:18 %S A200880 22,51,121,292,704,1691,4059,9749,23422,56268,135166,324692,779977, %T A200880 1873673,4500958,10812237,25973244,62393157,149881402,360046432, %U A200880 864906711,2077686532,4991036946,11989513056,28801314179,69186771332 %N A200880 Number of 0..2 arrays x(0..n+1) of n+2 elements without any interior element greater than both neighbors. %C A200880 Column 2 of A200886. %H A200880 R. H. Hardin, <a href="/A200880/b200880.txt">Table of n, a(n) for n = 1..210</a> %F A200880 Empirical: a(n) = 3*a(n-1) -3*a(n-2) +4*a(n-3) -a(n-4) +a(n-5). %F A200880 Empirical g.f.: x*(22 - 15*x + 34*x^2 - 6*x^3 + 9*x^4) / (1 - 3*x + 3*x^2 - 4*x^3 + x^4 - x^5). - _Colin Barker_, Oct 16 2017 %e A200880 Some solutions for n=3 %e A200880 ..2....0....2....0....2....1....2....2....2....1....1....1....0....2....2....1 %e A200880 ..0....2....1....0....1....2....2....1....2....2....0....1....0....2....2....2 %e A200880 ..1....2....0....2....1....2....0....2....0....2....1....1....1....1....2....2 %e A200880 ..1....0....1....2....0....1....1....2....0....2....1....1....1....0....1....1 %e A200880 ..0....1....2....0....1....1....1....1....1....2....1....0....1....1....2....2 %K A200880 nonn %O A200880 1,1 %A A200880 _R. H. Hardin_, Nov 23 2011