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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
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,5

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).

LINKS

Table of n, a(n) for n=1..31.

FORMULA

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

EXAMPLE

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.

Sequence in context: A005199 A107390 A051253 * A303526 A064403 A235344

Adjacent sequences:  A175952 A175953 A175954 * A175956 A175957 A175958

KEYWORD

nonn

AUTHOR

Max Alekseyev, Oct 29 2010

STATUS

approved

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Last modified June 19 05:18 EDT 2021. Contains 345125 sequences. (Running on oeis4.)