Problem Statement  
The prime factorization of a number X is the list of prime numbers that multiply together to form X. For example, the prime factorization of 12 is 2 * 2 * 3. Note that 1 is not a prime number. An underprime is a number whose prime factorization contains a prime number of elements. For example, 12 is an underprime because its prime factorization contains 3 elements, and 3 is a prime number. Given ints A and B, return the number of underprimes between A and B, inclusive.  
Definition  
 
Notes  
  A positive integer number is called prime if it has exactly two divisors  1 and itself. For example, 2, 3, 5 and 7 are prime numbers, and 4, 6, 8 and 9 are not prime. By convention, 1 is not considered to be a prime number.  
  All prime factorizations of the same integer always contain the same prime numbers and can only differ by the order of primes within them.  
Constraints  
  A will be between 2 and 100000, inclusive.  
  B will be between A and 100000, inclusive.  
Examples  
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