A221442 Hilltop maps: number of n X 4 binary arrays indicating the locations of corresponding elements not exceeded by any horizontal or antidiagonal neighbor in a random 0..1 n X 4 array.

9, 117, 1465, 18393, 230845, 2897357, 36364977, 456419681, 5728560373, 71899621813, 902417942313, 11326320232169, 142157556964077, 1784230940565533, 22394026158604769, 281069224947245681

Offset

1,1

Comments

Column 4 of A221446.

Links

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

Formula

Empirical: a(n) = 9*a(n-1) + 42*a(n-2) + 34*a(n-3) - 21*a(n-4) - 11*a(n-5) - 4*a(n-6).

Empirical g.f.: x*(9 + 36*x + 34*x^2 - 12*x^3 - 11*x^4 - 8*x^5) / (1 - 9*x - 42*x^2 - 34*x^3 + 21*x^4 + 11*x^5 + 4*x^6). - Colin Barker, Aug 05 2018

Example

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

Crossrefs

Cf. A221446.

Sequence in context: A092913 A022607 A139740 * A196663 A292843 A180904

Adjacent sequences: A221439 A221440 A221441 * A221443 A221444 A221445

Keyword

nonn

Author

R. H. Hardin, Jan 17 2013

Status

approved