A225308 Number of n X 7 -1,1 arrays such that the sum over i=1..n, j=1..7 of i*x(i,j) is zero and rows are nondecreasing (ways to put 7 thrusters pointing east or west at each of n positions 1..n distance from the hinge of a south-pointing gate without turning the gate).

0, 0, 22, 122, 0, 0, 29638, 197440, 0, 0, 64811436, 458450486, 0, 0, 170747302728, 1245085560292, 0, 0, 497500354657954, 3694982212755606, 0, 0, 1544103180477715700, 11609994393282630090, 0, 0, 5004924971984927428464

Offset

1,3

Comments

Column 7 of A225310.

Links

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

Example

Some solutions for n=4
.-1.-1.-1.-1.-1.-1.-1...-1.-1.-1.-1.-1.-1..1...-1.-1.-1..1..1..1..1
.-1.-1.-1.-1.-1..1..1...-1.-1.-1.-1.-1.-1.-1...-1.-1..1..1..1..1..1
.-1.-1.-1.-1.-1.-1..1...-1..1..1..1..1..1..1...-1.-1.-1.-1..1..1..1
..1..1..1..1..1..1..1...-1.-1.-1..1..1..1..1...-1.-1.-1.-1..1..1..1

Crossrefs

Cf. A225310.

Sequence in context: A221698 A081931 A156293 * A043498 A108571 A247700

Adjacent sequences: A225305 A225306 A225307 * A225309 A225310 A225311

Keyword

nonn

Author

R. H. Hardin, May 05 2013

Status

approved