A193642 Number of arrays of -2..2 integers x(1..n) with every x(i) in a subsequence of length 1 or 2 with sum zero

1, 5, 13, 37, 105, 297, 841, 2381, 6741, 19085, 54033, 152977, 433105, 1226197, 3471581, 9828661, 27826681, 78782265, 223046553, 631484317, 1787844005, 5061703197, 14330578721, 40572407841, 114867676321, 325210747045

Offset

1,2

Comments

Column 2 of A193648

Links

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

Formula

Empirical: a(n) = 2*a(n-1) +2*a(n-2) +a(n-3).

Empirical: G.f.: -x*(1+3*x+x^2) / ( -1+2*x+2*x^2+x^3 ). - R. J. Mathar, Feb 19 2015

Example

Some solutions for n=6
..1....0...-1....0...-1...-2...-2....1....1...-2...-1....2...-1....1....2....0
.-1....0....1...-1....1....2....2...-1...-1....2....1...-2....1...-1...-2....1
..2...-1...-1....1...-2...-2...-1....2....1...-2....2....1....0...-1....2...-1
.-2....1...-2....0....2....0....1...-2...-1....0...-2...-1....1....1...-2....2
.-1...-1....2....1....1....0...-1....0...-2....2....0...-2...-1...-1....2...-2
..1....1....0...-1...-1....0....1....0....2...-2....0....2....0....0...-2....2

Crossrefs

Sequence in context: A232879 A269803 A298417 * A220709 A182312 A071100

Adjacent sequences: A193639 A193640 A193641 * A193643 A193644 A193645

Keyword

nonn

Author

R. H. Hardin Aug 02 2011

Status

approved