Semiprime numbers are natural numbers that are products of exactly two (possibly equal) [[prime_number|prime numbers]].


'''Semiprimes'''   are also known as:
:::*   '''semi-primes'''
:::*   '''biprimes'''
:::*   '''bi-primes'''
:::*   ''' ''2-almost'' '''   primes
:::* &nbsp; or simply: &nbsp; ''' ''P<sub>2</sub> '' '''



;Example:
   <big> 1679  =  23 &times; 73 </big>

(This particular number was chosen as the length of the [http://en.wikipedia.org/wiki/Arecibo_message Arecibo message]).


;Task;
Write a function determining whether a given number is semiprime.


;See also:
* The Wikipedia article: &nbsp; [http://mathworld.wolfram.com/Semiprime.html semiprime].
* The Wikipedia article: &nbsp; [http://mathworld.wolfram.com/AlmostPrime.html almost prime].
* The OEIS article: &nbsp; [http://oeis.org/A001358 semiprimes] &nbsp; which has a shorter definition: ''the product of two primes''.
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