A225309 Number of nX8 -1,1 arrays such that the sum over i=1..n,j=1..8 of i*x(i,j) is zero and rows are nondecreasing (ways to put 8 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)

1, 5, 27, 175, 1165, 8221, 60007, 449693, 3437315, 26700429, 210147859, 1672294243, 13432357463, 108761156653, 886785526897, 7274670122017, 59999774031797, 497244626964801, 4138638973241695, 34580160863858515, 289947745327853737

Offset

1,2

Comments

Column 8 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..1..1..1..1...-1.-1.-1.-1.-1..1..1..1

Crossrefs

Sequence in context: A201870 A091101 A185622 * A231091 A205774 A326094

Adjacent sequences: A225306 A225307 A225308 * A225310 A225311 A225312

Keyword

nonn

Author

R. H. Hardin May 05 2013

Status

approved