Sunday Times Teaser 2659 – Two by Two

by Peter G Chamberlain

The letters A to Z have each been given a different value between 0 and 25 inclusive in some order. Hence a three letter word could, for example, be represented by a number with three, four, five or six digits.

Using this representation it turns out that every digit in TWO is a prime and that TWO x TWO = FOUR.

What is the number FOUR?