Now some moderately more complicated programs to find teh prime numbers less than $$20\text{.}$$ We do not vouch for the quality of these, or even their correctness!
www.tutorialspoint.com/python-program-for-sieve-of-eratosthenes
www.tutorialspoint.com/cplusplus-program-to-implement-sieve-of-eratosthenes-to-generate-prime-numbers-between-given-range
www.tutorialspoint.com/Sieve-of-Eratosthenes-in-java