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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). 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,3
COMMENTS
Column 7 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
CROSSREFS
Cf. A225310.
Sequence in context: A221698 A081931 A156293 * A043498 A108571 A247700
KEYWORD
nonn
AUTHOR
R. H. Hardin, May 05 2013
STATUS
approved

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Last modified March 2 21:08 EST 2024. Contains 370498 sequences. (Running on oeis4.)