In Chinese, it is very regular to constitute other numerals after 10. In Persian, numerals from 30,40, 50, 60, 70 to 100, from 11-20 are irregular. I wonder why about the irregularity. Maybe it would help me to understand from eliciting English 13 I wonder why it is thirteen for 13 intead of threeteen when people coined a new word. Why did they make the spelling irregular?