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 A221460 #10 Jun 02 2025 08:20:54
%S A221460 0,2,9,80,875,11880,192080,3608576,77295141,1860100000,49701143855,
%T A221460 1460328321024,46805373800640,1625353003293824,60796114850390625,
%U A221460 2437185999638364160,104248664384022862523,4739500894223556407808
%N A221460 Number of 0..n arrays of length n with each element unequal to at least one neighbor, starting with 0.
%C A221460 Diagonal of A221463.
%H A221460 R. H. Hardin, <a href="/A221460/b221460.txt">Table of n, a(n) for n = 1..71</a>
%F A221460 a(n) = [x^n] 1/(1 - x*Sum_{k>=1} n^k*x^k). - _Ilya Gutkovskiy_, Mar 21 2018
%e A221460 Some solutions for n=6
%e A221460 ..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
%e A221460 ..2....4....5....6....4....1....3....4....1....2....5....5....2....6....2....3
%e A221460 ..3....0....5....0....3....5....1....1....2....2....3....4....3....4....3....4
%e A221460 ..6....3....2....1....1....6....2....2....6....4....6....5....4....1....6....1
%e A221460 ..2....6....3....0....3....4....6....3....3....0....1....1....2....2....5....5
%e A221460 ..0....2....2....1....6....1....1....6....1....4....4....5....4....5....2....3
%Y A221460 Cf. A221463.
%K A221460 nonn
%O A221460 1,2
%A A221460 _R. H. Hardin_ Jan 17 2013