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A175954 Unlabeled (cyclic) Motzkin numbers: number of ways of drawing any number of nonintersecting chords joining n unlabeled points equally spaced on a circle, up to rotations of the circle. 3
1, 1, 2, 2, 4, 5, 12, 19, 46, 95, 230, 528, 1320, 3219, 8172, 20714, 53478, 138635, 363486, 957858, 2543476, 6788019, 18218772, 49120019, 133036406, 361736109, 987316658, 2703991820, 7429445752, 20473889133, 56579632732, 156766505691 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Unlabeled version of A001006.

The number of such chord configurations on 2n vertices with n chords is given by A002995(n+1).

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..200

Andrew Howroyd, Chord Configuration Symmetries

FORMULA

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

a(n) = (1/n) * (A001006(n) + A142150(n) * A001006(n/2-1) + Sum{d|n, d<n} totient(n/d) * A002426(d)). - Andrew Howroyd, Apr 01 2017

CROSSREFS

Cf. A001006, A185100, A002426, A002995.

Sequence in context: A103420 A032258 A153949 * A158649 A019964 A087377

Adjacent sequences:  A175951 A175952 A175953 * A175955 A175956 A175957

KEYWORD

nonn

AUTHOR

Max Alekseyev, Oct 29 2010

STATUS

approved

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Last modified November 21 16:27 EST 2017. Contains 295003 sequences.