0,4

Equivalently, the number of closed convex paths of length n whose steps are the 15th roots of unity up to translation.

Andrew Howroyd, Table of n, a(n) for n = 0..1000

G.f.: (1 - x^15)/((1 - x^3)^5 * (1 - x^5)^3).

(PARI) Vec((1 - x^15)/((1 - x^3)^5 * (1 - x^5)^3) + O(x^50))

Cf. A198805, A321419.

Sequence in context: A182567 A339457 A300728 * A225424 A202626 A011995

Adjacent sequences: A321415 A321416 A321417 * A321419 A321420 A321421

nonn,easy

Andrew Howroyd, Nov 09 2018

approved