A225304 Number of nX3 -1,1 arrays such that the sum over i=1..n,j=1..3 of i*x(i,j) is zero and rows are nondecreasing (ways to put 3 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).
0, 0, 6, 16, 0, 0, 474, 1576, 0, 0, 64700, 228876, 0, 0, 10659862, 38869960, 0, 0, 1941920508, 7211917300, 0, 0, 376790653888, 1416598649968, 0, 0, 76344225166632, 289560610889154, 0, 0, 15965033749025502, 60953934482465398, 0, 0
Offset: 1
Keywords
Examples
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
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Comments