# Prime Tester

cehsu

1,464 views

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

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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;

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## Optimize

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?

See:

https://github.com/AlgorithmsMeetup/GetAllPrimes

How about non-deterministic approaches?

See:

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