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 A269649 #5 Mar 02 2016 11:25:09 %S A269649 2,9,64,621,7686,115902,2061940,42277329,981592964,25455321375, %T A269649 729233710320,22870710513322,779384544768952,28676004488510379, %U A269649 1132947222095403840,47837636065465105365,2149808857973618974752 %N A269649 Number of length-n 0..n arrays with no adjacent pair x,x+1 repeated. %C A269649 Diagonal of A269656. %H A269649 R. H. Hardin, <a href="/A269649/b269649.txt">Table of n, a(n) for n = 1..20</a> %e A269649 Some solutions for n=6 %e A269649 ..6. .3. .1. .2. .4. .5. .2. .2. .4. .4. .6. .4. .4. .4. .0. .0 %e A269649 ..0. .3. .6. .2. .4. .3. .4. .1. .4. .4. .4. .2. .4. .0. .3. .6 %e A269649 ..5. .0. .0. .2. .5. .1. .1. .3. .3. .4. .4. .5. .4. .2. .6. .4 %e A269649 ..3. .0. .5. .4. .6. .5. .2. .1. .2. .5. .5. .3. .0. .5. .3. .5 %e A269649 ..5. .4. .3. .3. .3. .1. .0. .5. .0. .5. .0. .6. .4. .6. .5. .1 %e A269649 ..0. .6. .6. .0. .0. .5. .1. .4. .2. .4. .5. .3. .0. .0. .5. .0 %Y A269649 Cf. A269656. %K A269649 nonn %O A269649 1,1 %A A269649 _R. H. Hardin_, Mar 02 2016