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 A268938 #7 Mar 21 2018 11:42:38 %S A268938 3,9,24,63,159,396,969,2349,5640,13455,31911,75348,177225,415557, %T A268938 971808,2267631,5281359,12280860,28518153,66147165,153274488, %U A268938 354861711,820976631,1898144676,4386240393,10131006069,23390390544,53984735343 %N A268938 Number of length-n 0..2 arrays with no repeated value unequal to the previous repeated value plus one mod 2+1. %C A268938 Column 2 of A268944. %H A268938 R. H. Hardin, <a href="/A268938/b268938.txt">Table of n, a(n) for n = 1..210</a> %F A268938 Empirical: a(n) = 3*a(n-1) + a(n-2) - 6*a(n-3). %F A268938 Empirical g.f.: 3*x*(1 - 2*x^2) / ((1 - 2*x)*(1 - x - 3*x^2)). - _Colin Barker_, Mar 21 2018 %e A268938 Some solutions for n=9: %e A268938 ..0. .1. .2. .2. .2. .1. .2. .2. .0. .2. .1. .0. .0. .0. .0. .1 %e A268938 ..0. .2. .0. .1. .1. .0. .0. .0. .1. .1. .2. .2. .2. .2. .2. .0 %e A268938 ..2. .0. .2. .2. .2. .1. .1. .1. .0. .0. .1. .1. .0. .0. .0. .0 %e A268938 ..1. .2. .2. .0. .0. .0. .2. .1. .1. .0. .0. .2. .1. .0. .2. .2 %e A268938 ..0. .0. .0. .2. .0. .1. .0. .2. .0. .1. .0. .1. .0. .2. .0. .1 %e A268938 ..1. .2. .2. .2. .2. .1. .2. .1. .1. .1. .2. .0. .0. .0. .0. .1 %e A268938 ..0. .1. .0. .0. .0. .0. .1. .0. .2. .0. .0. .1. .1. .1. .2. .2 %e A268938 ..1. .0. .0. .2. .2. .2. .1. .2. .1. .2. .1. .2. .1. .1. .1. .2 %e A268938 ..2. .2. .2. .1. .1. .0. .0. .2. .2. .1. .0. .1. .0. .2. .2. .1 %Y A268938 Cf. A268944. %K A268938 nonn %O A268938 1,1 %A A268938 _R. H. Hardin_, Feb 16 2016