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A208638 Number of 3 X n 0..1 arrays with new values 0..1 introduced in row major order and no element equal to more than one of its immediate leftward or upward or right-upward antidiagonal neighbors. 2
4, 13, 32, 71, 150, 309, 628, 1267, 2546, 5105, 10224, 20463, 40942, 81901, 163820, 327659, 655338, 1310697, 2621416, 5242855, 10485734, 20971493, 41943012, 83886051, 167772130, 335544289, 671088608, 1342177247, 2684354526, 5368709085 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Row 3 of A208637. Possibly row 4 of the convolution array A213568. - Clark Kimberling, Jun 20 2012

LINKS

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

FORMULA

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

Conjectures from Colin Barker, Mar 07 2018: (Start)

G.f.: x*(4 - 3*x) / ((1 - x)^2*(1 - 2*x)).

a(n) = 5*2^n - n - 5.

(End)

EXAMPLE

Some solutions for n=4:

..0..1..0..1....0..0..1..0....0..1..0..0....0..0..0..1....0..0..0..0

..0..1..0..0....1..0..1..0....0..1..1..1....1..1..0..0....1..1..1..0

..1..0..1..0....1..0..1..0....1..0..0..1....0..1..1..1....0..0..1..1

CROSSREFS

Cf. A208637.

Sequence in context: A037235 A051912 A060099 * A173277 A036420 A266094

Adjacent sequences:  A208635 A208636 A208637 * A208639 A208640 A208641

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 29 2012

STATUS

approved

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Last modified February 18 10:22 EST 2019. Contains 320250 sequences. (Running on oeis4.)