UVa 884 – Factorial Factors

#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <cmath>

using namespace std;

int prime[1000001];
int visit[1000001];
int numbe[1000001];
int sums[1000001];

int main()
{
	//筛法计算素数 
	memset(visit, 0, sizeof(visit));
	memset(numbe, 0, sizeof(numbe));
	int count = 0;
	for (int i = 2 ; i < 1000001 ; ++ i) {
		if (!visit[i]) {
			prime[count ++] = i;
			numbe[i] = 1;
		}
		for (int j = 0 ; j < count && i*prime[j] < 1000001 ; ++ j) {
			visit[i*prime[j]] = 1;
			numbe[i*prime[j]] = numbe[i]+1;
		}
		sums[i] = sums[i-1] + numbe[i];
	}
	
	int n;
	while (~scanf("%d",&n))
		printf("%d\n",sums[n]);
		
    return 0;
}