A225307 - OEIS

A225307

Number of nX6 -1,1 arrays such that the sum over i=1..n,j=1..6 of i*x(i,j) is zero and rows are nondecreasing (ways to put 6 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, 3, 17, 83, 427, 2341, 13333, 77721, 461973, 2791167, 17087937, 105766229, 660771733, 4161393187, 26390549923, 168386196159, 1080202503299, 6962854947491, 45075011876699, 292931328936351, 1910374828122659

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

COMMENTS

Column 6 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