<Tr> <Td> 90 </Td> <Td> enneaconta - </Td> <Td> 9 </Td> <Td> - ennea - </Td> </Tr> <P> Extending the system up to 999 is expressed with these prefixes . </P> <Table> Polygon names <Tr> <Th_colspan="2"> Ones </Th> <Th_colspan="2"> Tens </Th> <Th_colspan="2"> Twenties </Th> <Th_colspan="2"> Thirties+ </Th> <Th_colspan="2"> Hundreds </Th> </Tr> <Tr> <Td> </Td> <Td> </Td> <Td> 10 </Td> <Td> deca - </Td> <Td> 20 </Td> <Td> icosa - </Td> <Td> 30 </Td> <Td> triaconta - </Td> <Td> 100 </Td> <Td> hecta - </Td> </Tr> <Tr> <Td> </Td> <Td> hena - </Td> <Td> 11 </Td> <Td> hendeca - </Td> <Td> 21 </Td> <Td> icosi - hena - </Td> <Td> 31 </Td> <Td> triaconta - hena - </Td> <Td> 200 </Td> <Td> dihecta - </Td> </Tr> <Tr> <Td> </Td> <Td> di - </Td> <Td> 12 </Td> <Td> dodeca - </Td> <Td> 22 </Td> <Td> icosi - di - </Td> <Td> 32 </Td> <Td> triaconta - di - </Td> <Td> 300 </Td> <Td> trihecta - </Td> </Tr> <Tr> <Td> </Td> <Td> tri - </Td> <Td> 13 </Td> <Td> triskaideca - </Td> <Td> 23 </Td> <Td> icosi - tri - </Td> <Td> 33 </Td> <Td> triaconta - tri - </Td> <Td> 400 </Td> <Td> tetrahecta - </Td> </Tr> <Tr> <Td> </Td> <Td> tetra - </Td> <Td> 14 </Td> <Td> tetrakaideca - </Td> <Td> 24 </Td> <Td> icosi - tetra - </Td> <Td> 40 </Td> <Td> tetraconta - </Td> <Td> 500 </Td> <Td> pentahecta - </Td> </Tr> <Tr> <Td> 5 </Td> <Td> penta - </Td> <Td> 15 </Td> <Td> pentakaideca - </Td> <Td> 25 </Td> <Td> icosi - penta - </Td> <Td> 50 </Td> <Td> pentaconta - </Td> <Td> 600 </Td> <Td> hexahecta - </Td> </Tr> <Tr> <Td> 6 </Td> <Td> hexa - </Td> <Td> 16 </Td> <Td> hexakaideca - </Td> <Td> 26 </Td> <Td> icosi - hexa - </Td> <Td> 60 </Td> <Td> hexaconta - </Td> <Td> 700 </Td> <Td> heptahecta - </Td> </Tr> <Tr> <Td> 7 </Td> <Td> hepta - </Td> <Td> 17 </Td> <Td> heptakaideca - </Td> <Td> 27 </Td> <Td> icosi - hepta - </Td> <Td> 70 </Td> <Td> heptaconta - </Td> <Td> 800 </Td> <Td> octahecta - </Td> </Tr> <Tr> <Td> 8 </Td> <Td> octa - </Td> <Td> 18 </Td> <Td> octakaideca - </Td> <Td> 28 </Td> <Td> icosi - octa - </Td> <Td> 80 </Td> <Td> octaconta - </Td> <Td> 900 </Td> <Td> enneahecta - </Td> </Tr> <Tr> <Td> 9 </Td> <Td> ennea - </Td> <Td> 19 </Td> <Td> enneakaideca - </Td> <Td> 29 </Td> <Td> icosi - ennea - </Td> <Td> 90 </Td> <Td> enneaconta - </Td> <Td> </Td> <Td> </Td> </Tr> </Table> <Tr> <Th_colspan="2"> Ones </Th> <Th_colspan="2"> Tens </Th> <Th_colspan="2"> Twenties </Th> <Th_colspan="2"> Thirties+ </Th> <Th_colspan="2"> Hundreds </Th> </Tr>

What is the name of a 21 sided polygon
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