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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 (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) = (1/24)*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(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5) 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 A277828

Adjacent sequences:  A227634 A227635 A227636 * A227638 A227639 A227640

KEYWORD

nonn

AUTHOR

R. H. Hardin, Jul 18 2013

STATUS

approved

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Last modified March 19 11:10 EDT 2019. Contains 321329 sequences. (Running on oeis4.)