A225315 Number of 8Xn -1,1 arrays such that the sum over i=1..8,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 8 positions 1..n distance from the hinge of a south-pointing gate without turning the gate).
14, 217, 1576, 7445, 26498, 77721, 197440, 449693, 939130, 1828785, 3360554, 5882479, 9878430, 16007047, 25142264, 38426053, 57321356, 83680907, 119814040, 168573865, 233439470, 318623729, 429172318, 571094583, 751480676, 978657917
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...-1..1..1..1...-1..1..1..1...-1.-1.-1.-1...-1..1..1..1 .-1..1..1..1....1..1..1..1....1..1..1..1....1..1..1..1...-1.-1..1..1 .-1.-1.-1..1...-1.-1.-1.-1...-1.-1.-1.-1...-1.-1.-1..1...-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
Formula
Empirical: a(n) = a(n-1) +a(n-2) -a(n-5) -a(n-7) -a(n-9) +a(n-11) +2*a(n-12) +a(n-13) +a(n-15) -a(n-16) -a(n-17) -2*a(n-18) -a(n-19) -a(n-20) +a(n-21) +a(n-23) +2*a(n-24) +a(n-25) -a(n-27) -a(n-29) -a(n-31) +a(n-34) +a(n-35) -a(n-36)
Comments