A226866 Number of n X 2 (-1,0,1) arrays of determinants of 2 X 2 subblocks of some (n+1) X 3 binary array with rows and columns of the latter in lexicographically nondecreasing order.

4, 13, 37, 91, 199, 397, 736, 1285, 2134, 3397, 5215, 7759, 11233, 15877, 21970, 29833, 39832, 52381, 67945, 87043, 110251, 138205, 171604, 211213, 257866, 312469, 376003, 449527, 534181, 631189, 741862, 867601, 1009900, 1170349, 1350637

Offset

1,1

Links

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

Formula

Empirical: a(n) = (1/40)*n^5 + (7/8)*n^3 + (21/10)*n + 1.

Conjectures from Colin Barker, Sep 06 2018: (Start)

G.f.: x*(4 - 11*x + 19*x^2 - 16*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..0....0..0....0..0...-1..0....0..0...-1..1...-1..0....0.-1....0.-1
..0.-1....0.-1....0..0....0..0....0..0....0.-1....1.-1....1..0....0..0...-1..0
..0..0....0..1....0.-1...-1..1....1..0...-1..0....0..0....0..0....0..1....0..0
.-1..0...-1.-1...-1.-1....0..0....0..0....1..0....0..0....0..0...-1.-1....0..0

Crossrefs

Column 2 of A226870.

Sequence in context: A279111 A299111 A324250 * A048474 A054761 A244197

Adjacent sequences: A226863 A226864 A226865 * A226867 A226868 A226869

Keyword

nonn

Author

R. H. Hardin Jun 20 2013

Status

approved