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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. 1
81, 399, 1620, 6462, 26481, 110769, 469617, 2009553, 8655441, 37451697, 162572721, 707284113, 3081856785, 13442980209, 58681197681, 256284824145, 1119691708881, 4893034223409, 21386003380017, 93482466850833, 408662174944401 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 21 02:29 EDT 2021. Contains 348141 sequences. (Running on oeis4.)