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

Author

R. H. Hardin, Nov 23 2011

Keywords

• nonn

Comments

Column 2 of A200886.

Examples

			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
		

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