A193696 Number of arrays of -2..2 integers x(1..n) with every x(i) in a subsequence of length 1, 2 or 3 with sum zero.

1, 5, 23, 83, 299, 1081, 3931, 14293, 51955, 188859, 686519, 2495537, 9071325, 32974351, 119862177, 435700975, 1583780905, 5757072535, 20927062737, 76070247573, 276516705575, 1005143149813, 3653713262601, 13281312856865

Offset: 1

Author

R. H. Hardin Aug 02 2011

Keywords

• nonn

Comments

Column 2 of A193702

Examples

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

Links

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

Formula

Empirical: a(n) = 3*a(n-1) +2*a(n-2) -2*a(n-3) +5*a(n-4) +16*a(n-5) +18*a(n-6) +20*a(n-7) +23*a(n-8) +18*a(n-9) +7*a(n-10) +a(n-11) +4*a(n-12) +7*a(n-13) +a(n-14) -7*a(n-15) -8*a(n-16) -4*a(n-17) -a(n-18)