Count 11 to 20

 If you want to learn more, here are 11 through 20.
 

11. e{ndeka

12. dwvdeka (or dekaduvo)

13. treiskaivdeka (or trei:V kai; devka)

14. dekatevssareV

15. dekapevnte (or pentekaivdeka)

16. eJkkaivdeka

17. eJptakaivdeka

18. dekaoktwv (or ojktwkai;deka)

19. ejnneakaivdeka

20. ei[kosi(n)
 

You can probably figure out who the Greeks put these letters together from the smaller numbers.