A225305 Number of nX4 -1,1 arrays such that the sum over i=1..n,j=1..4 of i*x(i,j) is zero and rows are nondecreasing (ways to put 4 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, 9, 31, 113, 443, 1787, 7445, 31593, 136351, 596187, 2636015, 11763569, 52920569, 239731317, 1092632909, 5006816043, 23053197067, 106601983853, 494856940025, 2305237337415, 10772988573393, 50491926308985
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
Links
- R. H. Hardin, Table of n, a(n) for n = 1..210
Comments