OFFSET
0,4
COMMENTS
Equivalently, the number of closed convex paths of length n whose steps are the 15th roots of unity up to translation.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..1000
FORMULA
G.f.: (1 - x^15)/((1 - x^3)^5 * (1 - x^5)^3).
PROG
(PARI) Vec((1 - x^15)/((1 - x^3)^5 * (1 - x^5)^3) + O(x^50))
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Andrew Howroyd, Nov 09 2018
STATUS
approved