JOIN

 Problem Statement

### Problem Statement

A number is preprime if it has exactly 4 positive integer divisors. For example, 6 is preprime because its divisors are 1, 2, 3, and 6. The integers 6, 8, 10, 14 form the beginning of an infinite sequence of preprime numbers. Find the n-th element of this sequence, where n is a 1-based index.

### Definition

 Class: PreprimeNumbers Method: nthNumber Parameters: int Returns: int Method signature: int nthNumber(int n) (be sure your method is public)

### Constraints

-n will be between 1 and 1000000, inclusive.

### Examples

0)

 `2`
`Returns: 8`
 The beginning of an infinite sequence of preprime numbers is: 6, 8, 10, 14, ... The second number is 8.
1)

 `4`
`Returns: 14`
 The beginning of an infinite sequence of preprime numbers is: 6, 8, 10, 14, ... The fourth number is 14.
2)

 `24`
`Returns: 77`
3)

 `43765`
`Returns: 193539`

This problem statement is the exclusive and proprietary property of TopCoder, Inc. Any unauthorized use or reproduction of this information without the prior written consent of TopCoder, Inc. is strictly prohibited. (c)2010, TopCoder, Inc. All rights reserved.

This problem was used for:
Single Round Match 307 Round 1 - Division II, Level Three