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A227252 Number of n X 2 binary arrays indicating whether each 2 X 2 subblock of a larger binary array has lexicographically nondecreasing rows and columns, for some larger (n+1) X 3 binary array with rows and columns of the latter in lexicographically nondecreasing order. 1
2, 3, 9, 23, 53, 113, 225, 421, 745, 1255, 2025, 3147, 4733, 6917, 9857, 13737, 18769, 25195, 33289, 43359, 55749, 70841, 89057, 110861, 136761, 167311, 203113, 244819, 293133, 348813, 412673, 485585, 568481, 662355, 768265, 887335, 1020757, 1169793 (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) = (1/60)*n^5 - (1/12)*n^4 + (5/12)*n^3 + (1/12)*n^2 - (13/30)*n + 1 for n>1.

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

G.f.: x*(2 - 9*x + 21*x^2 - 26*x^3 + 20*x^4 - 7*x^5 + x^6) / (1 - x)^6.

a(n) = 6*a(n-1) - 15*a(n-2) + 20*a(n-3) - 15*a(n-4) + 6*a(n-5) - a(n-6) for n>7.

(End)

EXAMPLE

Some solutions for n=4:

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

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

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

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

CROSSREFS

Column 2 of A227256.

Sequence in context: A294910 A111240 A298407 * A274495 A299705 A318231

Adjacent sequences:  A227249 A227250 A227251 * A227253 A227254 A227255

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 04 2013

STATUS

approved

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Last modified October 18 02:23 EDT 2019. Contains 328135 sequences. (Running on oeis4.)