Problem 187

Semiprimes

A composite is a number containing at least two prime factors. For example, 15 = 3 5; 9 = 3 3; 12 = 2 2 3.

There are ten composites below thirty containing precisely two, not necessarily distinct, prime factors: 4, 6, 9, 10, 14, 15, 21, 22, 25, 26.

How many composite integers, `n` 10^{8}, have precisely two, not necessarily distinct, prime factors?

**
These problems are part of
Project Euler
and are licensed under
CC BY-NC-SA 2.0 UK
**