Primes Go

package main

import (
    "fmt"
    "os"
    "strconv"
    "time"
)

func main() {
    var max_n = int32(20_000)
    if len(os.Args) > 1 {
        if n, err := strconv.Atoi(os.Args[1]); err == nil {
            max_n = int32(n)
        }
    }
    t := time.Now()
    primes := make([]int32, 1, max_n)
    primes[0] = 2
    var check int32 = 3
    var index int32 = 1
    for index < max_n {
        is_prime := true
        for _, prime := range primes {
            if (check % prime) == 0 {
                is_prime = false
                break
            }
        }
        if is_prime {
            primes = append(primes, check)
            index += 1
        }
        check += 2
    }
    fmt.Println(len(primes))
    fmt.Println(time.Since(t))
}