2 - two - the second 12 - twelve - the twelfth
3 - three - the third 13 - thirteen - the thirteenth
4 - four - the fourth 14 - fourteen - the fourteenth
5 - five - the fifth 15 - fifteen - the fifteenth
6 - six - the sixth 16 - sixteen - the sixteenth
7 - seven - the seventh 17 - seventeen - the seventeenth
8 - eight - the eighth 18 - eighteen - the eighteenth
9 - nine - the ninth 19 - nineteen - the nineteenth
10- ten - the tenth 20 - twenty - the twentieth
http://www.primarygames.com/squigly/congrats.htm
http://www.agendaweb.org/vocabulary/numbers-exercises.html