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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

%I #13 Mar 13 2019 05:20:54

%S 1,0,1,1,4,6,18,36,92,209,527,1269,3218,8063,20701,53209,138634,

%T 362789,957857,2541735,6787960,18214250,49120018,133024306,361736098,

%U 987284765,2703991469,7429359867,20473889132,56579399002,156766505690

%N 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.

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

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

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

%e 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.

%Y Cf. A001006, A175954.

%K nonn

%O 1,5

%A _Max Alekseyev_, Oct 29 2010

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