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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
OFFSET
1,2
COMMENTS
Column 8 of A225310
LINKS
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 A367048
KEYWORD
nonn
AUTHOR
R. H. Hardin May 05 2013
STATUS
approved