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A185100 Dihedral unlabeled Motzkin numbers: number of ways of drawing any number of nonintersecting chords joining n unlabeled points equally spaced on a circle, up to rotations and reflections of the circle. 2
1, 1, 2, 2, 4, 5, 11, 16, 36, 65, 150, 312, 756, 1743, 4353, 10732, 27489, 70379, 183866, 481952, 1277784, 3402661, 9126689, 24584870, 66567924, 180939737, 493801694, 1352203202, 3715137460, 10237545525, 28291018283, 78384998904, 217715672036, 606103034821, 1691020991782, 4727601528674, 13242641322252, 37162431389051, 104469244613429 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

Unlabeled version of A001006. Another version is given by A175954.

LINKS

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

Andrew Howroyd, Chord Configuration Symmetries

FORMULA

a(2n+1) = (1/2) * (A175954(2n+1) + A005773(n+1)). - Andrew Howroyd, Apr 01 2017

a(2n) = (1/4) * (2 * A175954(2n) + A005773(n) + A005773(n+1) + A001006(n-1)) for n > 0. - Andrew Howroyd, Apr 01 2017

CROSSREFS

Cf. A001006, A175954, A175955, A005773.

Sequence in context: A095020 A290436 A127825 * A103420 A032258 A153949

Adjacent sequences:  A185097 A185098 A185099 * A185101 A185102 A185103

KEYWORD

nonn

AUTHOR

Max Alekseyev, Feb 07 2011

STATUS

approved

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Last modified November 20 12:30 EST 2017. Contains 294971 sequences.