A225340 Number of nX4 -1,1 arrays such that the sum over i=1..n,j=1..4 of i*x(i,j) is zero, the sum of x(i,j) is zero, and rows are nondecreasing (number of ways to distribute 4-across galley oarsmen left-right at n fore-aft positions so that there are no turning moments on the ship)

1, 1, 3, 9, 31, 107, 395, 1525, 6095, 24893, 103583, 437763, 1874497, 8116459, 35485099, 156453779, 694956997, 3107415563, 13976787615, 63201012187, 287163163723, 1310481411725, 6004334305049, 27611237977705, 127399143883589

Offset

1,3

Comments

Column 4 of A225345

Links

R. H. Hardin, Table of n, a(n) for n = 1..135

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

Crossrefs

Sequence in context: A148965 A130620 A202246 * A148966 A279971 A127927

Adjacent sequences: A225337 A225338 A225339 * A225341 A225342 A225343

Keyword

nonn

Author

R. H. Hardin May 05 2013

Status

approved