A218805 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..3 n X 3 array.

7, 61, 481, 3843, 30719, 245509, 1962145, 15681787, 125331399, 1001668973, 8005501761, 63981275411, 511348785535, 4086782871861, 32662235081409, 261041908504267, 2086289496897799, 16673965838688029, 133261053752673313

Offset

1,1

Comments

Column 3 of A218810.

Links

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

Formula

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

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

Example

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

Crossrefs

Cf. A218810.

Sequence in context: A129079 A249556 A135165 * A164943 A218228 A155599

Adjacent sequences: A218802 A218803 A218804 * A218806 A218807 A218808

Keyword

nonn

Author

R. H. Hardin, Nov 06 2012

Status

approved