FWIW, this[1] is closer to how a "real" sieve of Eratosthenes program might look like, with three optimizations: 1) omitting even numbers from the sieve, 2) sie

FWIW, this[1] is closer to how a "real" sieve of Eratosthenes program might look like, with three optimizations: 1) omitting even numbers from the sieve, 2) sieving starting at n^2, 3) precomputing primes up to sqrt(n) if you want to sieve up to n. The code size then is Θ(sqrt(pi(n)). [1] https://jsfiddle.net/L8mxuag5/1/ https://jsfiddle.net/L8mxuag5/1/