A221447 Hilltop maps: number of 2 X n binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 2 X n array.

1, 9, 33, 117, 429, 1577, 5785, 21217, 77825, 285473, 1047145, 3841029, 14089277, 51680881, 189570641, 695364065, 2550664929, 9356094041, 34319088593, 125885849013, 461761883309, 1693788766169, 6212986580521, 22789856102913

Offset

1,2

Comments

Row 2 of A221446.

Links

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

Formula

Empirical: a(n) = 3*a(n-1) + a(n-2) + 5*a(n-3) + a(n-4) + a(n-5) - a(n-6) - a(n-7).

Empirical g.f.: x*(1 + 6*x + 5*x^2 + 4*x^3 - x^4 - 2*x^5 - x^6) / ((1 + x^2)*(1 - 3*x - 2*x^2 - 2*x^3 + x^4 + x^5)). - Colin Barker, Aug 05 2018

Example

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

Crossrefs

Cf. A221446.

Sequence in context: A147155 A146232 A146180 * A147147 A147154 A257284

Adjacent sequences: A221444 A221445 A221446 * A221448 A221449 A221450

Keyword

nonn

Author

R. H. Hardin, Jan 17 2013

Status

approved