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Last active November 15, 2017 09:44
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Calculate primes till certain number, checking against the already calculated, and only with the ones higher than the sqrt
function primes(max) {
let calculated = [1, 2, 3]; // already calculated primes
let num = 4; // current number being checked
let factors; // factors for the given number
let sqrt; // sqrt for a given number
// if the input is too low to be calculated, just return the default primes
if (max < 5) return calculated;
// otherwhise calculate for each number till you reach max
while (num < max) {
// discard even numbers
if (num % 2 == 1) {
sqrt = Math.sqrt(num); // calculate the sqrt only once per number
const factors = calculated
.filter(el=> el >= sqrt) // discard candidate if lower than the number sqrt
.filter(el=>num % el == 0); // discard candidate if not a factor
// if we found no factor then it's a prime!
if (factors.length == 0) calculated.push(num);
return calculated;
//const p = primes(10000);
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