

A227637


Number of n X 2 0,1 arrays indicating 2 X 2 subblocks of some larger (n+1) X 3 binary array having determinant equal to one, with rows and columns of the latter in nondecreasing lexicographic order.


1



2, 5, 11, 23, 44, 78, 130, 206, 313, 459, 653, 905, 1226, 1628, 2124, 2728, 3455, 4321, 5343, 6539, 7928, 9530, 11366, 13458, 15829, 18503, 21505, 24861, 28598, 32744, 37328, 42380, 47931, 54013, 60659, 67903, 75780, 84326, 93578, 103574, 114353
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OFFSET

1,1


LINKS

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


FORMULA

Empirical: a(n) = (1/24)*n^4  (1/12)*n^3 + (35/24)*n^2  (29/12)*n + 4 for n>1.
Conjectures from Colin Barker, Sep 09 2018: (Start)
G.f.: x*(2  5*x + 6*x^2  2*x^3  x^4 + x^5) / (1  x)^5.
a(n) = 5*a(n1)  10*a(n2) + 10*a(n3)  5*a(n4) + a(n5) for n>5.
(End)


EXAMPLE

Some solutions for n=4:
..0..0....0..0....0..0....0..1....0..0....0..0....0..0....0..1....0..0....0..0
..0..1....0..0....0..0....0..0....0..1....0..1....0..1....1..0....0..0....0..1
..0..0....0..0....1..0....1..0....0..0....0..1....1..0....0..0....0..0....0..1
..0..1....1..0....0..0....0..0....0..0....0..0....0..0....0..1....0..1....1..0


CROSSREFS

Column 2 of A227641.
Sequence in context: A281969 A124920 A064934 * A171985 A005986 A333396
Adjacent sequences: A227634 A227635 A227636 * A227638 A227639 A227640


KEYWORD

nonn


AUTHOR

R. H. Hardin, Jul 18 2013


STATUS

approved



