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 A269651 #4 Mar 02 2016 11:26:34 %S A269651 4,16,64,253,988,3816,14596,55344,208196,777582,2885120,10640607, %T A269651 39027196,142415244,517252820,1870499543,6736838192,24172420350, %U A269651 86428990624,308016010824,1094338584760,3876828265788,13696906252336 %N A269651 Number of length-n 0..3 arrays with no adjacent pair x,x+1 repeated. %C A269651 Column 3 of A269656. %H A269651 R. H. Hardin, <a href="/A269651/b269651.txt">Table of n, a(n) for n = 1..210</a> %F A269651 Empirical: a(n) = 16*a(n-1) -108*a(n-2) +408*a(n-3) -986*a(n-4) +1704*a(n-5) -2312*a(n-6) +2560*a(n-7) -2355*a(n-8) +1832*a(n-9) -1208*a(n-10) +672*a(n-11) -314*a(n-12) +120*a(n-13) -36*a(n-14) +8*a(n-15) -a(n-16) %e A269651 Some solutions for n=8 %e A269651 ..3. .0. .1. .1. .1. .1. .0. .1. .2. .2. .2. .2. .3. .3. .1. .3 %e A269651 ..1. .2. .1. .2. .3. .3. .3. .0. .0. .2. .1. .0. .3. .1. .3. .3 %e A269651 ..3. .2. .0. .3. .1. .2. .3. .3. .2. .2. .2. .1. .0. .1. .0. .1 %e A269651 ..2. .3. .0. .0. .0. .0. .2. .1. .3. .1. .1. .2. .2. .1. .1. .0 %e A269651 ..1. .0. .3. .2. .1. .3. .2. .3. .1. .0. .3. .0. .1. .3. .1. .0 %e A269651 ..3. .1. .3. .0. .2. .1. .3. .3. .3. .1. .1. .2. .1. .1. .2. .0 %e A269651 ..2. .3. .0. .0. .0. .0. .2. .2. .3. .1. .3. .2. .0. .2. .3. .1 %e A269651 ..2. .3. .0. .3. .2. .0. .0. .1. .3. .3. .3. .0. .3. .3. .1. .0 %Y A269651 Cf. A269656. %K A269651 nonn %O A269651 1,1 %A A269651 _R. H. Hardin_, Mar 02 2016