light oj 1098 数学规律

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <iostream>
#include <algorithm>
#include <climits>
#include <queue>
#define ll long long

using namespace std;


const ll MAX = (ll)sqrt(2e9)+1;
const ll MOD = 1e9+7;

ll ok(ll a1, ll an, ll d)
{
    return ((an-a1)/d+1)*(a1+an)/2;
}

void solve()
{
    ll n,k;
    ll sum = 0;
    scanf("%lld",&n);
    k = (ll)sqrt(n);

    for(ll i = 2; i <= k; i++)
    {
        sum += i*(n/i-1);
        if(i < n/i)
            sum += (i-1) * ok(n/(i+1)+1, n/i, 1);
    }

    printf("%lld\n",sum);
}
int  main(void)
{

    ll t,cnt = 0;
    scanf("%lld",&t);
    while(t--)
    {
        printf("Case %lld: ",++cnt);
        solve();
    }
    return 0;
}