A square-free integer is an integer which is indivisible by any square number except 11. For example, 6 = 2 \cdot 36=2⋅3 is square-free, but 12 = 2^2 \cdot 312=22⋅3 is not, because 2^222 is a square number. Some integers could be decomposed into product of two square-free integers, there may be more than one decomposition ways. For example, 6 = 1\cdot 6=6 \cdot 1=2\cdot 3=3\cdot 2, n=ab6=1⋅6=6⋅1=2⋅3=3⋅2,n=ab and n=ban=ba are considered different if a \not = ba=b. f(n)f(n) is the number of decomposition ways that n=abn=ab such that aaand bb are square-free integers. The problem is calculating \sum_{i = 1}^nf(i)∑i=1nf(i).
Input
The first line contains an integer T(T\le 20)T(T≤20), denoting the number of test cases.
For each test case, there first line has a integer n(n \le 2\cdot 10^7)n(n≤2⋅107).
Output
For each test case, print the answer \sum_{i = 1}^n f(i)∑i=1nf(i).
Hint
\sum_{i = 1}^8 f(i)=f(1)+ \cdots +f(8)∑i=18f(i)=f(1)+⋯+f(8)
=1+2+2+1+2+4+2+0=14=1+2+2+1+2+4+2+0=14.
样例输入
2 5 8
样例输出
8 14
题目来源
欧拉筛法学习。
代码:
#include <iostream> #define MAX 10000000 using namespace std; int t; int n; int num[MAX * 2 + 1],sum[MAX * 2 + 1]; bool vis[MAX * 2 + 1]; int prime[MAX + 1]; void init() { sum[1] = num[1] = 1; for(int i = 2;i <= MAX * 2;i ++) { if(!vis[i]) { prime[++ prime[0]] = i; num[i] = 2; } for(int j = 1;j <= prime[0] && i * prime[j] <= MAX * 2;j ++) { vis[i * prime[j]] = true; if(i % prime[j] == 0) { if(i / prime[j] % prime[j]) num[i * prime[j]] = num[i / prime[j]]; break; } num[i * prime[j]] = num[i] * num[prime[j]]; } sum[i] += sum[i - 1] + num[i]; } } int main() { scanf("%d",&t); init(); while(t --) { scanf("%d",&n); printf("%d\n",sum[n]); } return 0; }