login
A133129
Number of black/white colorings of a 3 X n rectangle which have no monochromatic 2 by 2 subsquares.
3
1, 8, 50, 322, 2066, 13262, 85126, 546410, 3507314, 22512862, 144506294, 927561722, 5953863490, 38216853518, 245307588134, 1574588362378, 10107019231634, 64875265300670, 416423472774166, 2672952594083738, 17157235452223586, 110129423550044398
OFFSET
0,2
FORMULA
G.f.: 1+x*(8+2*x-2*x^2)/(1-6*x-3*x^2+2*x^3). - Colin Barker, Jan 04 2012
EXAMPLE
a(2) = 50 because if the middle row is not monochromatic, the top and bottom rows are unconstrained, contributing 2*4*4. if the middle row is monochromatic, the top and bottom rows can each take on only 3 values contributing 2*3*3.
CROSSREFS
Column k=3 of A181245.
Sequence in context: A287812 A180029 A357479 * A103458 A339687 A238841
KEYWORD
nonn
AUTHOR
Victor S. Miller, Sep 19 2007
EXTENSIONS
More terms from Colin Barker, Jan 03 2012
a(0)=1 prepended and g.f. adapted by Alois P. Heinz, Feb 19 2015
STATUS
approved