Latin Numbers!

One=unus

Two=duo

Three=tres

Four=quattour

Five=quinque

Six=sex

Seven=septem

Eight=octo

Nine=novem

Ten=decem

From here on it follows a simple pattern...

Eleven=undecem

Twelve=duodecem

Thirteen=tredecem

Fourteen=quadecem

Fifteen=quindecem

Sixteen=sedecem

Seventeen=sepdecem

Here is where it changes a little bit:

Eighteen=duo de viginti

Nineteen=unus de viginti

Twenty=viginti

And the pattern repeats...