The primes up to n

Problem

A prime number can only be divided by 1 and by itself. The 1 does not count as prime: the first one is 2.

Write a function that takes a number n and returns the list of the primes from 2 up to n, from smallest to largest. If n is prime, it goes in too. With n smaller than 2 there are none, so you return an empty list.

An old trick to do it without dividing so much: write down every number from 2 to n and cross out the multiples of each prime you find. What is left uncrossed is the answer.

Examples

• Nothing before 2

  1 → []

• The first prime

  2 → [2]

• Up to 10

  10 → [2, 3, 5, 7]

• n is prime

  13 → [2, 3, 5, 7, 11, 13]

Besides these, the challenge has hidden tests that are revealed when you submit your solution.

You start with this

def primes_up_to(n):
    pass

function primesUpTo(n) {
}