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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. 4
 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

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Last modified June 20 21:52 EDT 2021. Contains 345264 sequences. (Running on oeis4.)