A225304 Number of nX3 -1,1 arrays such that the sum over i=1..n,j=1..3 of i*x(i,j) is zero and rows are nondecreasing (ways to put 3 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, 6, 16, 0, 0, 474, 1576, 0, 0, 64700, 228876, 0, 0, 10659862, 38869960, 0, 0, 1941920508, 7211917300, 0, 0, 376790653888, 1416598649968, 0, 0, 76344225166632, 289560610889154, 0, 0, 15965033749025502, 60953934482465398, 0, 0

Offset

1,3

Comments

Column 3 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

Sequence in context: A280964 A191463 A235943 * A299709 A107777 A136140

Adjacent sequences: A225301 A225302 A225303 * A225305 A225306 A225307

Keyword

nonn

Author

R. H. Hardin May 05 2013

Status

approved