Generating prime numbers:

There are many methods for generating prime numbers (for details see: https://en.wikipedia.org/wiki/Generating_primes#Prime_sieves)

Today you will implement one of it:
https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes

Task:
Write the function which given the 'n' return all primes equal or smaller than 'n'.

a) naive version: checks iteratively until n with modulo division

b) use "Sieve of Eratosthenes" algorithm

Compare the complexity of a) and b)