RSA Numbers

A number is an RSA number if it has exactly four divisors — that is, exactly four positive integers divide it evenly. For example, $10$ is an RSA number because it has exactly four divisors ($1, 2, 5, 10$). $12$ is not an RSA number because it has too many divisors ($1, 2, 3, 4, 6, 12$), and $11$ is not one either (its only divisors are $1$ and $11$). So there is exactly one RSA number in the range $10 \dots 12$.

Write a program that reads a range of numbers and counts how many numbers in that range are RSA numbers. You may assume that every number in the range is less than $1000$.

(The name comes from the RSA encryption that many web browsers use to protect information such as credit-card numbers sent over the Internet.)

Two integers $a$ and $b$ ($a \le b$) are given: the inclusive lower and upper bounds of the range. Each number is less than $1000$.

Print a single line in exactly the following form:

The number of RSA numbers between a and b is c

where $a$ and $b$ are the given bounds and $c$ is the number of RSA numbers in the range $[a, b]$.