A221441 Hilltop maps: number of n X 3 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 n X 3 array.

5, 33, 221, 1473, 9829, 65569, 437437, 2918273, 19468741, 129882145, 866485149, 5780598081, 38564209189, 257274109985, 1716357449085, 11450366664449, 76389039372165, 509615587618849, 3399807737852509, 22681199192442049

Offset: 1

Author

R. H. Hardin, Jan 17 2013

Keywords

• nonn

Comments

Column 3 of A221446.

Examples

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

Links

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

Crossrefs

Cf. A221446.

Formula

Empirical: a(n) = 5*a(n-1) + 11*a(n-2) + a(n-3).

Empirical g.f.: x*(5 + 8*x + x^2) / (1 - 5*x - 11*x^2 - x^3). - Colin Barker, Aug 05 2018