A188242 Number of arrangements of n+2 nonzero numbers x(i) in -2..2 with the sum of x(i)*x(i+1) equal to zero.

16, 20, 120, 300, 1284, 4132, 16272, 57808, 223308, 828456, 3193588, 12106616, 46777036, 179484068, 695670728, 2689241588, 10454975104, 40616587968, 158328346172, 617266507080, 2411727117520, 9427476168776, 36906793159556

Offset

1,1

Comments

Column 2 of A188249

Links

R. H. Hardin, Table of n, a(n) for n = 1..200

Example

Some solutions for n=4
.-2...-1...-1....2....2...-1....1...-1...-2....1....1...-1....1...-1....2...-2
..2....2...-1....1....1....2...-1....2....2...-2...-1....1....1....2....2....1
..1....1....1...-1....1....1....1....2....1...-1...-1....1...-2...-2...-1....2
.-1....1....2....1...-2...-2....2...-1....2....2...-2...-1...-2...-2....2...-1
.-1....1...-2....2....1...-2...-1...-2....2....2....2....1....1...-2....1....2
.-2...-2...-1...-1....1....1...-2....1...-2...-1....1....2...-1....1...-2....2

Crossrefs

Sequence in context: A219395 A260572 A240038 * A103330 A045667 A045658

Adjacent sequences: A188239 A188240 A188241 * A188243 A188244 A188245

Keyword

nonn

Author

R. H. Hardin, Mar 25 2011

Status

approved