A208820 Number of n-bead necklaces labeled with numbers -3..3 allowing reversal, with sum zero.

1, 4, 8, 38, 155, 828, 4390, 25202, 146803, 878708, 5330524, 32785934, 203687695, 1276913732, 8065359582, 51282069040

Offset: 1

Author

R. H. Hardin, Mar 01 2012

Keywords

• nonn

Comments

Column 3 of A208825.

Examples

			All solutions for n=3:
.-2....0...-2...-3...-1...-3...-1...-2
.-1....0....1....1...-1....0....0....0
..3....0....1....2....2....3....1....2