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A227554 Number of n X 2 0,1 arrays indicating 2 X 2 subblocks of some larger (n+1) X 3 binary array having nonzero determinant, with rows and columns of the latter in lexicographically nondecreasing order. 1
4, 12, 33, 81, 179, 362, 680, 1201, 2014, 3232, 4995, 7473, 10869, 15422, 21410, 29153, 39016, 51412, 66805, 85713, 108711, 136434, 169580, 208913, 255266, 309544, 372727, 445873, 530121, 626694, 736902, 862145, 1003916, 1163804, 1343497 (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) = (1/40)*n^5 + (17/24)*n^3 + (34/15)*n + 1.

Conjectures from Colin Barker, Sep 08 2018: (Start)

G.f.: x*(4 - 12*x + 21*x^2 - 17*x^3 + 8*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=4:

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

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

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

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

CROSSREFS

Column 2 of A227558.

Sequence in context: A168078 A225894 A318637 * A305778 A104747 A070050

Adjacent sequences:  A227551 A227552 A227553 * A227555 A227556 A227557

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 16 2013

STATUS

approved

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Last modified November 21 14:18 EST 2019. Contains 329371 sequences. (Running on oeis4.)