An 11sided polygon is called either a undecagon or a hendecagon. The sum of the interior angles of this polygon is 1620 degrees. It also has 44 diagonals. You can find more information
http://answers.ask.com/Science/Mathematics/what_is...

hendecagon.
http://wiki.answers.com/Q/What_are_polygons_with_1...

The proposed name for an 11 sided polygon is Undecagon or Hendecagon.
http://www.chacha.com/question/what'sa11sidedp...

A 11 sided polygon is called Undecagon and Hendecagon. A 21 sided polygon is called "icosikaihenagon.
http://www.kgbanswers.com/whatisan11sidedpoly...
