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 A217880 #9 Jul 23 2018 08:45:33 %S A217880 3,9,22,46,86,148,244,402,685,1223,2263,4243,7910,14528,26274,47012, %T A217880 83787,149619,268568,484722,878014,1592150,2884434,5215660,9413514, %U A217880 16970286,30584282,55140634,99481417,179592631,324338478,585786560 %N A217880 Number of n element 0..2 arrays with each element the minimum of 5 adjacent elements of a random 0..2 array of n+4 elements. %C A217880 Column 5 of A217883. %H A217880 R. H. Hardin, <a href="/A217880/b217880.txt">Table of n, a(n) for n = 1..210</a> %F A217880 Empirical: a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) + 3*a(n-6) - a(n-7) + a(n-8) + a(n-9) + a(n-10) + a(n-11). %F A217880 Empirical g.f.: x*(1 + x^2 + x^3 + x^4 + x^5)*(3 + x^2 + x^3 + x^4 + x^5) / ((1 - x + x^3 + x^4 + x^5)*(1 - 2*x + x^2 - x^3 - x^6)). - _Colin Barker_, Jul 23 2018 %e A217880 Some solutions for n=4: %e A217880 ..0....2....1....0....0....1....0....0....0....1....0....2....1....0....0....2 %e A217880 ..0....2....1....2....0....2....1....2....0....1....1....0....2....0....0....2 %e A217880 ..2....0....0....2....1....2....1....1....1....2....2....0....2....1....0....2 %e A217880 ..1....0....0....0....2....1....2....1....0....1....2....0....0....1....2....0 %Y A217880 Cf. A217883. %K A217880 nonn %O A217880 1,1 %A A217880 _R. H. Hardin_, Oct 14 2012