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A225976 Number of n X 2 binary arrays whose sum with another n X 2 binary array containing no more than two 1s has rows and columns in lexicographically nondecreasing order. 1
4, 15, 48, 138, 350, 790, 1616, 3049, 5384, 9001, 14376, 22092, 32850, 47480, 66952, 92387, 125068, 166451, 218176, 282078, 360198, 454794, 568352, 703597, 863504, 1051309, 1270520, 1524928, 1818618, 2155980, 2541720, 2980871, 3478804, 4041239 (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) = (11/120)*n^5 - (1/8)*n^4 + (9/8)*n^3 - (7/8)*n^2 + (287/60)*n - 1.

Conjectures from Colin Barker, Sep 05 2018: (Start)

G.f.: x*(4 - 9*x + 18*x^2 - 5*x^3 + 2*x^4 + x^5) / (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>6.

(End)

EXAMPLE

Some solutions for n=3:

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

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

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

CROSSREFS

Column 2 of A225982.

Sequence in context: A238807 A240333 A227099 * A093967 A052201 A320460

Adjacent sequences:  A225973 A225974 A225975 * A225977 A225978 A225979

KEYWORD

nonn

AUTHOR

R. H. Hardin, May 22 2013

STATUS

approved

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Last modified January 28 00:32 EST 2020. Contains 331313 sequences. (Running on oeis4.)