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n N-gon
3 Triangle
4 Quadrilateral
5 Pentagon
6 Hexagon
7 Heptagon
8 Octagon
10 Decagon
12 Dodecagon
Names for other polygons have been proposed:
Sides Name
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9 Nonagon, Enneagon
11 Undecagon, Hendecagon
13 Tridecagon, Triskaidecagon
14 Tetradecagon, Tetrakaidecagon
15 Pentadecagon, Pentakaidecagon
16 Hexadecagon, Hexakaidecagon
17 Heptadecagon, Heptakaidecagon
18 Octadecagon, Octakaidecagon
19 Enneadecagon, Enneakaidecagon
20 Icosagon
30 Triacontagon
40 Tetracontagon
50 Pentacontagon
60 Hexacontagon
70 Heptacontagon
80 Octacontagon
90 Enneacontagon
100 Hectogon, Hecatontagon
1,000 Chiliagon
10,000 Myriagon
Eternity.