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 A267226 #10 Feb 06 2018 04:16:32 %S A267226 3,9,21,47,103,223,479,1023,2175,4607,9727,20479,43007,90111,188415, %T A267226 393215,819199,1703935,3538943,7340031,15204351,31457279,65011711, %U A267226 134217727,276824063,570425343,1174405119,2415919103,4966055935 %N A267226 Number of length-n 0..2 arrays with no following elements greater than or equal to the first repeated value. %C A267226 Column 2 of A267232. %H A267226 R. H. Hardin, <a href="/A267226/b267226.txt">Table of n, a(n) for n = 1..210</a> %F A267226 Empirical: a(n) = 5*a(n-1) -8*a(n-2) +4*a(n-3) for n>4. %F A267226 Conjectures from _Colin Barker_, Feb 05 2018: (Start) %F A267226 G.f.: x*(3 - 6*x + 2*x^3) / ((1 - x)*(1 - 2*x)^2). %F A267226 a(n) = 2^(n+1) + 2^(n-2)*n - 1 for n>1. %F A267226 (End) %e A267226 Some solutions for n=6: %e A267226 1 0 0 1 2 0 1 2 1 1 0 2 1 1 2 2 %e A267226 0 2 1 2 0 2 2 1 0 2 2 1 2 0 0 1 %e A267226 2 2 2 0 1 0 1 2 1 1 0 0 0 2 2 0 %e A267226 0 0 0 2 2 1 2 0 0 2 1 1 2 2 2 1 %e A267226 2 0 2 1 1 1 0 2 1 1 0 1 0 1 1 2 %e A267226 1 1 1 1 0 0 1 1 1 1 2 0 1 1 0 0 %Y A267226 Cf. A267232. %K A267226 nonn %O A267226 1,1 %A A267226 _R. H. Hardin_, Jan 12 2016