A255628 Number of length n+6 0..2 arrays with at most two downsteps in every n consecutive neighbor pairs.

2187, 6561, 19683, 51768, 114546, 225253, 405687, 685713, 1103630, 1707576, 2557098, 3724906, 5298831, 7384008, 10105306, 13610028, 18070905, 23689409, 30699411, 39371211, 50015968, 62990559, 78702897, 97617739, 120263016

Offset

1,1

Comments

Row 6 of A255622.

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = (1/40320)*n^8 + (1/480)*n^7 + (13/192)*n^6 + (67/12)*n^5 + (48663/640)*n^4 + (46699/480)*n^3 + (5325055/2016)*n^2 - (53947/8)*n + 3866 for n>4.

Example

Some solutions for n=4
..2....0....2....1....2....0....1....0....1....0....1....0....2....1....0....2
..1....2....1....2....1....1....2....0....2....0....2....2....2....1....0....1
..0....2....2....0....1....0....2....0....0....2....0....1....2....1....2....2
..1....2....0....1....1....0....0....1....1....0....0....1....2....1....1....1
..1....2....1....0....1....1....0....1....0....2....1....2....1....0....2....2
..2....0....0....2....1....1....1....0....1....1....2....0....0....1....1....0
..0....2....0....0....1....0....2....1....2....2....2....0....1....1....1....0
..0....1....2....1....0....2....2....0....2....1....0....0....1....1....0....0
..1....1....0....0....0....1....0....1....0....2....1....0....2....2....0....0
..2....1....2....1....1....1....0....1....1....2....2....1....0....1....2....0

Crossrefs

Cf. A255622.

Sequence in context: A046320 A232926 A255113 * A232287 A219134 A233160

Adjacent sequences: A255625 A255626 A255627 * A255629 A255630 A255631

Keyword

nonn

Author

R. H. Hardin, Feb 28 2015

Status

approved