A206535 Number of (n+1) X 2 0..2 arrays with the number of clockwise edge increases in 2 X 2 subblocks nondecreasing, and counterclockwise edge increases nonincreasing, rightwards and downwards.

81, 399, 1620, 6462, 26481, 110769, 469617, 2009553, 8655441, 37451697, 162572721, 707284113, 3081856785, 13442980209, 58681197681, 256284824145, 1119691708881, 4893034223409, 21386003380017, 93482466850833, 408662174944401

Offset

1,1

Comments

Column 1 of A206542.

Links

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

Formula

Empirical: a(n) = 7*a(n-1) - 9*a(n-2) - 15*a(n-3) + 18*a(n-4) for n>8.

Empirical g.f.: 3*x*(27 - 56*x - 148*x^2 - 24*x^3 + 118*x^4 + 226*x^5 + 111*x^6 + 18*x^7) / ((1 - x)*(1 - 3*x)*(1 - 3*x - 6*x^2)). - Colin Barker, Jun 17 2018

Example

Some solutions for n=4:
..1..2....1..1....0..0....0..2....2..2....2..0....2..0....0..0....1..1....2..1
..1..2....0..0....1..1....1..1....2..0....2..2....2..2....0..2....1..1....0..2
..1..1....2..0....1..0....1..2....0..0....2..0....1..2....0..2....1..1....1..0
..2..1....0..0....0..0....0..0....1..0....2..2....2..2....2..2....1..1....2..1
..1..1....0..1....2..2....2..1....0..0....0..2....2..0....1..0....1..1....1..0

Crossrefs

Cf. A206542.

Sequence in context: A236719 A236712 A206542 * A017498 A097025 A074387

Adjacent sequences: A206532 A206533 A206534 * A206536 A206537 A206538

Keyword

nonn

Author

R. H. Hardin, Feb 09 2012

Status

approved