A221460 Number of 0..n arrays of length n with each element unequal to at least one neighbor, starting with 0.

0, 2, 9, 80, 875, 11880, 192080, 3608576, 77295141, 1860100000, 49701143855, 1460328321024, 46805373800640, 1625353003293824, 60796114850390625, 2437185999638364160, 104248664384022862523, 4739500894223556407808

Offset: 1

Author

R. H. Hardin Jan 17 2013

Keywords

• nonn

Comments

Diagonal of A221463.

Examples

			Some solutions for n=6
..0....0....0....0....0....0....0....0....0....0....0....0....0....0....0....0
..2....4....5....6....4....1....3....4....1....2....5....5....2....6....2....3
..3....0....5....0....3....5....1....1....2....2....3....4....3....4....3....4
..6....3....2....1....1....6....2....2....6....4....6....5....4....1....6....1
..2....6....3....0....3....4....6....3....3....0....1....1....2....2....5....5
..0....2....2....1....6....1....1....6....1....4....4....5....4....5....2....3
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..71

Crossrefs

Cf. A221463.

Formula

a(n) = [x^n] 1/(1 - x*Sum_{k>=1} n^k*x^k). - Ilya Gutkovskiy, Mar 21 2018