sieve of eratosthenes
function solution(n) {
const numArr = new Array(n + 1);
numArr.fill(true);
numArr[0] = numArr[1] = false;
for (let i = 2; i <= Math.sqrt(n); i++) {
for (let j = 2; i * j <= n; j++) {
numArr[i * j] = false;
}
}
return numArr.filter(Boolean).length;
}