September 6, 2019

We have on several occasions seen functions for generating the primes less than n. Sometimes, what you want instead of primes are semi-primes, numbers which are the product of two primes. For instance, the six semi-primes less than 25 are 2×3=6, 2×5=10, 2×7=14, 3×5=15, 3×7=21 and 2×11=22.

Your task is to write a function that makes a list of the semi-primes less than n; use it to discover the number of semi-primes less than 10,000. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.


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