A202963 Number of arrays of 3 integers in -n..n with sum zero and adjacent elements differing in absolute value.

2, 6, 20, 36, 62, 90, 128, 168, 218, 270, 332, 396, 470, 546, 632, 720, 818, 918, 1028, 1140, 1262, 1386, 1520, 1656, 1802, 1950, 2108, 2268, 2438, 2610, 2792, 2976, 3170, 3366, 3572, 3780, 3998, 4218, 4448, 4680, 4922, 5166, 5420, 5676, 5942, 6210, 6488

Offset: 1

Author

R. H. Hardin, Dec 26 2011

Keywords

• nonn

Examples

			Some solutions for n=5
.-2....1....3...-4...-2...-4....5...-1...-1....2....2....2...-2....2....1....4
.-3....0....1....1...-1....3...-1....5....2...-4....0....1....3....3...-2...-1
..5...-1...-4....3....3....1...-4...-4...-1....2...-2...-3...-1...-5....1...-3
		

Links

• R. H. Hardin, Table of n, a(n) for n = 1..210

Crossrefs

Row 1 of A202962.

Formula

Empirical: a(n) = 2*a(n-1) -2*a(n-3) +a(n-4).

Empirical g.f.: x*(2+2*x+8*x^2)/(1-2*x+2*x^3-x^4). - Colin Barker, Jan 04 2012