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.


link "factors"
 
procedure main(A)
    every nf := semiprime(n := !A) do write(n," = ",nf[1]," * ",nf[2])
end
 
procedure semiprime(n)  # Succeeds and produces the factors only if n is semiprime.
    return (2 = *(nf := factors(n)), nf)
end