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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
OFFSET
1,1
LINKS
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 A343561 A104747
KEYWORD
nonn
AUTHOR
R. H. Hardin, Jul 16 2013
STATUS
approved