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

1,1

Comments

Row 1 of A202962

Links

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

Formula

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

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

Example

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

Crossrefs

Sequence in context: A181558 A218883 A353699 * A130315 A087150 A323724

Adjacent sequences: A202960 A202961 A202962 * A202964 A202965 A202966

Keyword

nonn

Author

R. H. Hardin Dec 26 2011

Status

approved