A207694 - OEIS

A207694

Number of 3 X n 0..1 arrays avoiding 0 0 0 and 0 1 0 horizontally and 0 0 1 and 1 1 1 vertically.

6, 36, 60, 100, 240, 576, 1296, 2916, 6804, 15876, 36288, 82944, 191808, 443556, 1018980, 2340900, 5397840, 12446784, 28640304, 65901924, 151822836, 349764804, 805233312, 1853819136, 4269519072, 9833102244, 22641659460, 52134588900

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OFFSET

1,1

COMMENTS

Row 3 of A207693.

LINKS

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

FORMULA

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

Empirical g.f.: 2*x*(3 + 15*x + 12*x^2 + 11*x^3 - 11*x^4 - 84*x^5 - 60*x^6) / ((1 + 3*x^2)*(1 - x - 3*x^2)). - Colin Barker, Mar 05 2018

EXAMPLE

Some solutions for n=4:

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

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

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

CROSSREFS

Cf. A207693.

Sequence in context: A178909 A206982 A121026 * A208496 A207584 A207590

Adjacent sequences: A207691 A207692 A207693 * A207695 A207696 A207697

KEYWORD

nonn

AUTHOR

R. H. Hardin, Feb 19 2012

STATUS

approved