给定一个n,注意这里n小于10^12,求从i=1到n, n%i之和
import java.math.BigInteger;
import java.util.Scanner;
import java.math.*;
public class Main
{
public static BigInteger Solve(long n)
{
BigInteger ans=BigInteger.ZERO;
long i,t=(long) Math.sqrt(n*1.0);
for(i=1L;i<=t;i++)
{
BigInteger a=BigInteger.valueOf(n/i+n/(i+1)+1);
BigInteger b=BigInteger.valueOf(n/i-n/(i+1));
BigInteger temp=BigInteger.ZERO;
if(i!=(n/i))
temp= (a.multiply(b)).divide(BigInteger.valueOf(2));
BigInteger c=BigInteger.valueOf(n/i);
BigInteger ret=c.add(temp);
ret=ret.multiply(BigInteger.valueOf(i));
ans=ans.add(ret);
}
return ans;
}
public static void main(String[] args)
{
Scanner cin = new Scanner(System.in);
while(cin.hasNextLong())
{
long n=cin.nextLong();
BigInteger x=BigInteger.valueOf(n);
System.out.println((x.multiply(x)).subtract(Solve(n)));
}
}
}