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 A200881 #10 Oct 16 2017 12:22:46 %S A200881 50,144,422,1268,3823,11472,34350,102896,308419,924532,2771101, %T A200881 8305373,24892609,74608516,223618304,670231838,2008825312,6020872062, %U A200881 18045827096,54087163859,162110668160,485879938474,1456284886944,4364793695063 %N A200881 Number of 0..3 arrays x(0..n+1) of n+2 elements without any interior element greater than both neighbors. %C A200881 Column 3 of A200886. %H A200881 R. H. Hardin, <a href="/A200881/b200881.txt">Table of n, a(n) for n = 1..210</a> %F A200881 Empirical: a(n) = 4*a(n-1) -6*a(n-2) +10*a(n-3) -5*a(n-4) +6*a(n-5) -a(n-6) +a(n-7). %F A200881 Empirical g.f.: x*(50 - 56*x + 146*x^2 - 56*x^3 + 93*x^4 - 12*x^5 + 16*x^6) / (1 - 4*x + 6*x^2 - 10*x^3 + 5*x^4 - 6*x^5 + x^6 - x^7). - _Colin Barker_, Oct 16 2017 %e A200881 Some solutions for n=3 %e A200881 ..2....2....2....3....0....3....1....1....3....3....1....3....0....1....3....1 %e A200881 ..0....2....1....2....0....3....1....2....2....3....0....3....1....1....1....2 %e A200881 ..2....1....0....0....2....3....0....2....1....1....1....1....3....0....3....3 %e A200881 ..2....2....0....1....3....3....2....0....2....1....2....0....3....0....3....3 %e A200881 ..0....2....2....2....3....2....3....3....3....2....3....3....1....3....3....3 %K A200881 nonn %O A200881 1,1 %A A200881 _R. H. Hardin_, Nov 23 2011