C++ :

#include<iostream>
//#include<time.h>
#include<cmath>
using namespace std;

int IsPrime(int n){
    int i;
        if (n==1) return 0;
        if (n==2) return 1;
    if(n%2==0) return 0;
    for(i = 3;i <= sqrt(n);i+=2){
        if(n%i==0) return 0;
    }
    return 1; 
}

int main(){
    int n,i;
    cin >> n;
    //int t1 = clock();
    for(i = 1;i<=n;i++){
        if(IsPrime(i)) printf("%d ",i);
    }
    //int t2 = clock();
    //printf("\n运行时间：%d\n",t2-t1);
}

Python :

# coding=utf-8
a=int(input())
for i in range(2,a+1,1):
    n=2
    k=1
    import math
    b=math.sqrt(i)
    while n<=b:
        if i%n==0:
            k=0
            break
        n=n+1
    if k==1:
        print(i)