A200880 Number of 0..2 arrays x(0..n+1) of n+2 elements without any interior element greater than both neighbors.

22, 51, 121, 292, 704, 1691, 4059, 9749, 23422, 56268, 135166, 324692, 779977, 1873673, 4500958, 10812237, 25973244, 62393157, 149881402, 360046432, 864906711, 2077686532, 4991036946, 11989513056, 28801314179, 69186771332

Offset

1,1

Comments

Column 2 of A200886.

Links

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

Formula

Empirical: a(n) = 3*a(n-1) -3*a(n-2) +4*a(n-3) -a(n-4) +a(n-5).

Empirical g.f.: x*(22 - 15*x + 34*x^2 - 6*x^3 + 9*x^4) / (1 - 3*x + 3*x^2 - 4*x^3 + x^4 - x^5). - Colin Barker, Oct 16 2017

Example

Some solutions for n=3
..2....0....2....0....2....1....2....2....2....1....1....1....0....2....2....1
..0....2....1....0....1....2....2....1....2....2....0....1....0....2....2....2
..1....2....0....2....1....2....0....2....0....2....1....1....1....1....2....2
..1....0....1....2....0....1....1....2....0....2....1....1....1....0....1....1
..0....1....2....0....1....1....1....1....1....2....1....0....1....1....2....2

Crossrefs

Sequence in context: A015226 A092221 A191279 * A330409 A111576 A277979

Adjacent sequences: A200877 A200878 A200879 * A200881 A200882 A200883

Keyword

nonn

Author

R. H. Hardin, Nov 23 2011

Status

approved