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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
1, 5, 27, 175, 1165, 8221, 60007, 449693, 3437315, 26700429, 210147859, 1672294243, 13432357463, 108761156653, 886785526897, 7274670122017, 59999774031797, 497244626964801, 4138638973241695, 34580160863858515, 289947745327853737 (list; graph; refs; listen; history; text; internal format)
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

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Last modified November 29 08:27 EST 2020. Contains 338761 sequences. (Running on oeis4.)