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 A337700 Place two n-gons with radii 1 and 2 concentrically, forming an annular area between them. Connect all the vertices with line segments that lie entirely within that area. Then a(n) is the number of regions in that figure. 4
 12, 16, 20, 24, 63, 72, 315, 350, 385, 408, 767, 826, 2085, 2224, 2363, 2340, 3762, 3960, 7644, 8008, 8372, 8448, 11850, 12324, 20466, 21224, 21982, 21480, 28985, 29920, 45177, 46546, 47915, 48456, 60273, 61902, 87555, 89800, 92045, 91896, 111972, 114576 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,1 COMMENTS Because of symmetry, a(n) is divisible by n. LINKS Lars Blomberg, Table of n, a(n) for n = 3..102 Lars Blomberg, Illustration for n = 3 Lars Blomberg, Illustration for n = 4 Lars Blomberg, Illustration for n = 5 Lars Blomberg, Illustration for n = 7 Lars Blomberg, Illustration for n = 10 Lars Blomberg, Illustration for n = 29 Lars Blomberg, Illustration for n = 32 FORMULA a(n) = A337702(n) - A337701(n) by Euler's formula, there being 1 hole. CROSSREFS Cf. A337701, A337702, A337703. Sequence in context: A210577 A231903 A337703 * A243538 A183052 A344079 Adjacent sequences:  A337697 A337698 A337699 * A337701 A337702 A337703 KEYWORD nonn AUTHOR Lars Blomberg, Sep 16 2020 STATUS approved

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Last modified January 26 07:15 EST 2022. Contains 350573 sequences. (Running on oeis4.)