A218804 Hilltop maps: number of n X 2 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..3 n X 2 array.

3, 15, 57, 225, 895, 3551, 14089, 55905, 221827, 880191, 3492529, 13858081, 54987775, 218187167, 865749521, 3435226017, 13630706691, 54085572239, 214607297385, 851544879425, 3378863116543, 13407063134527, 53198172193817

Offset

1,1

Comments

Column 2 of A218810.

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) + 3*a(n-3) + a(n-4) + a(n-5) + a(n-6) + a(n-7).

Empirical g.f.: x*(1 + x)^2*(3 + x^4) / (1 - 3*x - 3*x^2 - 3*x^3 - x^4 - x^5 - x^6 - x^7). - Colin Barker, Jul 24 2018

Example

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

Crossrefs

Cf. A218810.

Sequence in context: A210448 A284699 A218657 * A125673 A123007 A121695

Adjacent sequences: A218801 A218802 A218803 * A218805 A218806 A218807

Keyword

nonn

Author

R. H. Hardin, Nov 06 2012

Status

approved