A225314 Number of 7Xn -1,1 arrays such that the sum over i=1..7,j=1..n of i*x(i,j) is zero and rows are nondecreasing (ways to put n thrusters pointing east or west at each of 7 positions 1..n distance from the hinge of a south-pointing gate without turning the gate)

8, 87, 474, 1787, 5304, 13333, 29638, 60007, 112790, 199669, 336342, 543465, 847456, 1281681, 1887330, 2714817, 3824812, 5289809, 7195252, 9641399, 12744472, 16638757, 21477906, 27437211, 34714980, 43535143, 54148610, 66836145, 81909858

Offset

1,1

Comments

Row 7 of A225310

Links

R. H. Hardin, Table of n, a(n) for n = 1..210

Formula

Empirical: a(n) = 3*a(n-2) +2*a(n-3) -3*a(n-4) -5*a(n-5) +4*a(n-7) +a(n-8) -2*a(n-9) +a(n-10) +3*a(n-11) -3*a(n-13) -a(n-14) +2*a(n-15) -a(n-16) -4*a(n-17) +5*a(n-19) +3*a(n-20) -2*a(n-21) -3*a(n-22) +a(n-24)

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....1..1..1..1
..1..1..1..1...-1.-1..1..1...-1..1..1..1...-1..1..1..1....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: A202545 A131812 A241259 * A200767 A222513 A307822

Adjacent sequences: A225311 A225312 A225313 * A225315 A225316 A225317

Keyword

nonn

Author

R. H. Hardin May 05 2013

Status

approved