A hendecagon has how many sides?

In geometry, a hendecagon (also undecagon or endecagon) or 11-gon is an eleven-sided polygon. The name hendecagon, from Greek "hendeka" ("eleven") and "gon" ("corner"), is often preferred to the hybrid undecagon, whose first part is formed from Latin "undecim" ("eleven").

As 11 is not a Fermat prime, the regular hendecagon is not constructible with compass and straightedge. Because 11 is not a Pierpont prime, construction of a regular hendecagon is still impossible even with the usage of an angle trisector.

The Canadian dollar coin, the loonie, is similar to, but not exactly, a regular hendecagonal prism, as are the Indian 2-rupee coin and several other lesser-used coins of other nations. The cross-section of a loonie is actually a Reuleaux hendecagon. The United States Susan B. Anthony dollar has a hendecagonal outline along the inside of its edges.