Solution: Goroutines

package main
import (
	"fmt"
	"math"
	"sync"
)
var (
	mu sync.Mutex
)
func isPrime(num int) bool {
	for i := 2; i <= int(math.Sqrt(float64(num))); i++ {
		if int(num)%i == 0 {
			return false
		}
	}
	return true
}
func findPrimes(resultMap map[int]struct{}, startFrom, tryCount int, wg *sync.WaitGroup) {
	for i := startFrom; i < startFrom+tryCount; i++ {
		if isPrime(i) {
			mu.Lock()
			resultMap[i] = struct{}{}
			mu.Unlock()
		}
	}
	wg.Done()
}
func main() {
	resultMap := make(map[int]struct{})
	var wg sync.WaitGroup
	for i := 0; i < 100; i++ {
		wg.Add(1)
		go findPrimes(resultMap, 99999*i+2, 1000, &wg)
	}
	wg.Wait()
	fmt.Printf("Found %v primes\n", len(resultMap))
	if len(resultMap) < 6746 {
		panic("did not find all the prime numbers")
	}
}