

A337700


Place two ngons 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
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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



