A337702 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 edges in that figure.

21, 28, 35, 42, 112, 128, 567, 630, 693, 720, 1417, 1526, 3930, 4192, 4454, 4302, 7163, 7540, 14700, 15400, 16100, 16008, 22900, 23816, 39771, 41244, 42717, 40800, 56482, 58304, 88341, 91018, 93695, 94176, 118067, 121258, 171912, 176320, 180728, 178626

Offset

3,1

Comments

Because of symmetry, a(n) is divisible by n.

See A337700 for illustrations.

Links

Lars Blomberg, Table of n, a(n) for n = 3..102

Formula

a(n) = A337700(n) + A337701(n) by Euler's formula, there being 1 hole.

Crossrefs

Cf. A337700, A337701, A337703.

Sequence in context: A103083 A120735 A009727 * A168105 A227936 A048012

Adjacent sequences: A337699 A337700 A337701 * A337703 A337704 A337705

Keyword

nonn

Author

Lars Blomberg, Sep 16 2020

Status

approved