A175955 Number of ways to connect with nonintersecting chords n unlabeled points equally spaced on a circle such that the resulting configuration is not invariant w.r.t. rotation any angle < 2*Pi.

1, 0, 1, 1, 4, 6, 18, 36, 92, 209, 527, 1269, 3218, 8063, 20701, 53209, 138634, 362789, 957857, 2541735, 6787960, 18214250, 49120018, 133024306, 361736098, 987284765, 2703991469, 7429359867, 20473889132, 56579399002, 156766505690

Offset: 1

Author

Max Alekseyev, Oct 29 2010

Keywords

• nonn

Comments

Also, number of chord configurations on n vertices of the period n.

Number of such chord configurations on 2n vertices with n chords is given by A005354(n+1).

Examples

			For n=2, there are only two configurations possible: two diametrically located points on a circle connected or not connected with a chord. Since both these configurations are invariant w.r.t. rotation by angle Pi, a(2)=0.
		

Crossrefs

Cf. A001006, A175954.

Formula

For odd prime p, a(p) = (A001006(p)-1)/p = A175954(p)-1.