Octadecagon (Wikipedia)
In geometry, an octadecagon (or octakaidecagon) or 18-gon is an eighteen-sided polygon.- In geometry, a heptadecagon, septadecagon or 17-gon is a seventeen-sided polygon.
- Hexadecagon (Wikipedia)
In mathematics, a hexadecagon (sometimes called a hexakaidecagon or 16-gon) is a sixteen-sided polygon.