Prime Tester


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The goal today is to write a function that determines whether a number is prime.

Check if a number is prime

Write an isPrime function that takes a number as parameter and returns true if this number is prime, false if it isn't.

Reminder: A prime number:

  • Can only be divided by 1 and itself
  • Is greater than 1
Write the isPrime function
function isPrime (number) {
return false;
// For demo purpose:
var start = 2;
while (start <= Math.sqrt(number)) {
if (number % start++ < 1) return false;
return number > 1;
module.exports = isPrime;


Take a look at the Sieve of Eratosthenes. How much faster did your implementation of the sieve run? How can you account for this in terms of time complexity?


How about non-deterministic approaches?


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