Numbers 11-19 

eleven - once

twelve - doce

thirteen - trece

fourteen - catorce

fifteen - quince

sixteen - dieciséis

seventeen - diecisiete

eighteen - dieciocho

nineteen - diecinueve

Numbers 20-31 

twenty - veinte

twenty-one - veintiuno (veinte y uno)

twenty-two - veintidós

twenty-three - veintitrés

twenty-four - veinticuatro

twenty-five - veinticinco

twenty-six - veintisé

twenty-seven - veintisiete

twenty-eight - veintiocho

twenty-nine - veintinueve

thirty - treinta

thirty-one - treintaiuno (treinta y uno)