A055610 A companion sequence to A011896.

0, 0, 0, 1, 2, 5, 9, 15, 24, 36, 52, 71, 95, 123, 156, 195, 240, 292, 350, 416, 489, 570, 660, 759, 868, 986, 1115, 1254, 1404, 1566, 1740, 1927, 2126, 2339, 2565, 2805, 3060, 3330, 3616, 3917, 4235, 4569, 4920, 5289, 5676, 6082, 6506, 6950, 7413, 7896

Offset: 0

Author

Michael Somos, Jun 02 2000

Keywords

• nonn
• easy

Examples

			x^3 + 2*x^4 + 5*x^5 + 9*x^6 + 15*x^7 + 24*x^8 + 36*x^9 + 52*x^10 + ...
		

Links

• Index entries for linear recurrences with constant coefficients, signature (3,-3,1,0,0,0,1,-3,3,-1).

Crossrefs

Cf. A011896.

Programs

PARI

a(n) = ceil( n * (n-1) * (n-2) / 14)

Formula

G.f.: x^3 * (1 - x + 2*x^2 - x^3 + x^4 + x^5) / ((1 - x)^3 * (1 - x^7)).

a(n) = -A011896(2 - n).