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A251212 Number of (n+1) X (1+1) 0..1 arrays with no 2 X 2 subblock having zero or two 1s. 1
9, 21, 49, 115, 269, 631, 1477, 3463, 8109, 19007, 44517, 104327, 244381, 572655, 1341525, 3143383, 7364173, 17254655, 40424581, 94714855, 221903869, 519914127, 1218099893, 2853948663, 6686519981, 15666114847, 36704297445, 85995716871 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

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

FORMULA

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

Empirical g.f.: x*(9 + 12*x - 8*x^2) / (1 - x - 4*x^2 + 2*x^3). - Colin Barker, Nov 27 2018

EXAMPLE

Some solutions for n=4:

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

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

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

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

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

CROSSREFS

Column 1 of A251219.

Sequence in context: A256530 A118130 A144482 * A176896 A134717 A216980

Adjacent sequences:  A251209 A251210 A251211 * A251213 A251214 A251215

KEYWORD

nonn

AUTHOR

R. H. Hardin, Nov 30 2014

STATUS

approved

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Last modified May 12 11:55 EDT 2021. Contains 343821 sequences. (Running on oeis4.)