A337701 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 vertices in that figure.

9, 12, 15, 18, 49, 56, 252, 280, 308, 312, 650, 700, 1845, 1968, 2091, 1962, 3401, 3580, 7056, 7392, 7728, 7560, 11050, 11492, 19305, 20020, 20735, 19320, 27497, 28384, 43164, 44472, 45780, 45720, 57794, 59356, 84357, 86520, 88683, 86730, 108145, 110660

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) = A337702(n) - A337700(n) by Euler's formula, there being 1 hole.

Crossrefs

Cf. A337700, A337702, A337703.

Sequence in context: A308748 A120167 A263674 * A048699 A019468 A084799

Adjacent sequences: A337698 A337699 A337700 * A337702 A337703 A337704

Keyword

nonn

Author

Lars Blomberg, Sep 16 2020

Status

approved