A218420 Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal, vertical or antidiagonal neighbor in a random 0..1 n X 2 array.

3, 13, 49, 191, 737, 2849, 11011, 42557, 164481, 635711, 2456993, 9496161, 36702211, 141852301, 548252401, 2118969471, 8189716289, 31652864193, 122336815619, 472825977597, 1827449929601, 7063007117695, 27298186799297, 105506194473793

Offset: 1

Author

R. H. Hardin, Oct 28 2012

Keywords

• nonn

Comments

Column 2 of A218426.

Examples

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

Links

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

Crossrefs

Cf. A218426.

Formula

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

Empirical g.f.: x*(3 + 4*x + x^2 + 2*x^3 + x^4) / (1 - 3*x - 3*x^2 - x^3 - x^4 - x^5). - Colin Barker, Mar 10 2018