The first two MU-numbers are 2 and 3. Every other MU-number is the smallest number not yet appeared that can be expressed as the product of two earlier distinct MU-numbers in exactly one way.
Here are the first 10
2, 3, 6, 12, 18, 24, 48, 54, 96, 162
Task
Given a positive number calculate and output the nth MU-number.
This is a code-golf competition so you should aim to make your source code as small as possible.