5 penta
6 hexa
7 hepta
8 octa
9 ennea
10 deca
11 hendeca
12 dodeca
13 triskaideca
14 tetrakaideca
15 pentakaideca
16 hexakaideca
17 heptakaideca
18 octakaideca
19 enneakaideca
20 icosa

isn't the web a wonderful thing...