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 A221455 #7 Aug 05 2018 08:23:09 %S A221455 0,1,2,7,25,101,436,1971,9159,43262,206285,988963,4755888,22910979, %T A221455 110480787,533057462,2572761417,12419474751,59958562568,289483787719, %U A221455 1397691920591,6748491159958,32584154032229,157329000870907 %N A221455 Number of 0..4 arrays of length n with each element unequal to at least one neighbor, with new values introduced in 0..4 order. %C A221455 Column 4 of A221459. %H A221455 R. H. Hardin, <a href="/A221455/b221455.txt">Table of n, a(n) for n = 1..210</a> %F A221455 Empirical: a(n) = 7*a(n-1) - 7*a(n-2) - 20*a(n-3) + 10*a(n-4) + 24*a(n-5) + 8*a(n-6). %F A221455 Empirical g.f.: x^2*(1 - 5*x + 10*x^3 + 5*x^4) / ((1 - x - x^2)*(1 - 2*x - 2*x^2)*(1 - 4*x - 4*x^2)). - _Colin Barker_, Aug 05 2018 %e A221455 Some solutions for n=6: %e A221455 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0 %e A221455 ..1....1....1....1....1....1....1....1....1....1....1....1....1....1....1....1 %e A221455 ..1....2....0....0....2....2....2....2....2....2....2....0....2....0....1....2 %e A221455 ..0....1....2....2....1....3....2....1....0....3....0....0....3....2....2....0 %e A221455 ..1....1....2....3....3....4....3....3....1....0....3....2....2....2....3....3 %e A221455 ..0....2....3....1....2....0....4....0....0....2....2....1....1....0....2....1 %Y A221455 Cf. A221459. %K A221455 nonn %O A221455 1,3 %A A221455 _R. H. Hardin_, Jan 17 2013