（1）package tan;
import java.util.Scanner;
public class X {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
int n = sc.nextInt();
for(int i=1;i<=n;i++)
{
if(IsPrime(i))
System.out.print(i+"\t");
}
}
static boolean IsPrime(int x)
{
boolean b=false;
int i;
for (i = 2; i<x; i++)
{
if(x%i==0) break;
}
if (i==x)
b=true;
return b;
}
}
（2）
package tan;
import java.util.Scanner;
public class X {
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);
System.out.println("请输入");
int n = sc.nextInt();
int count = 0;
int sum = 0;
for(int i=1;i<n;i++){
if(i%7==0){
count++;
sum+=i;
}
}
System.out.println("1-"+n+"之间能被7整除的数有"+count+"个，他们的和是："+sum);
}
}
（3）
package tan;
import java.util.Scanner;
public class X {
public static void main(String[] args) {
System.out.print("输入整数:");
Scanner s = new Scanner(System.in);
int n = s.nextInt();
int row = n*2-1;
int onrow = row/2+1;
int downrow = row/2;
for (int i = 1; i <= onrow ; i++) {
for (int j = 1; j <=onrow-i; j++)
System.out.print(" ");
for (int k = 1; k <= 2*i-1; k++)
System.out.print("*");
System.out.println();
}
for (int i = 1; i <= downrow; i++) {
for (int j = 1; j <= i; j++)
System.out.print(" ");
for (int k = row-2; k >= 2*i-1; k--)
System.out.print("*");
System.out.println();
}
}
}
