Semiprime numbers are natural numbers that are products of exactly two (possibly equal) prime numbers.


Semiprimes   are also known as:

   semi-primes
   biprimes
   bi-primes
    2-almost    primes
   or simply:    P2  


Example
 
   1679  =  23 × 73  

(This particular number was chosen as the length of the Arecibo message).



Task

Write a function determining whether a given number is semiprime.



See also

 The Wikipedia article:  semiprime.
 The Wikipedia article:  almost prime.
 The OEIS sequence:  A001358: semiprimes  which has a shorter definition: the product of two primes.


 
static void Main(string[] args)
{
    //test some numbers
    for (int i = 0; i < 50; i++)
    {
        Console.WriteLine("{0}\t{1} ", i,isSemiPrime(i));
    }
    Console.ReadLine();
}
 
//returns true or false depending if input was considered semiprime
private static bool isSemiPrime(int c)
{
    int a = 2, b = 0;
    while (b < 3 && c != 1)
    {
        if ((c % a) == 0)
        {
            c /= a;
            b++;
        }
        else
        {
            a++;
        };
    }
    return b == 2;
}
 