Other than veinte, they all end in -enta.Learn the numbers for the multiples of ten: veinte, treinta, cuarenta, cincuenta, sesenta, setenta, ochenta, noventa.There's no real pattern, you just have to learn them: uno, dos, tres, cuatro, cinco, seis, siete, ocho, nueve, diez, once, doce, trece, catorce, quince. I recommend you follow these steps to get all the numbers into your head: Take a look and try to spot the patterns.