C 华华给月月出题 积性函数

https://ac.nowcoder.com/acm/contest/392/C

 

 

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int mod = 1e9 + 7;
const int maxn = 1.3e7 + 5;
int prime[maxn], n;
ll sum[maxn];
bool v[maxn];
ll quickpow(ll x,ll y)
{
    ll res = 1;
    while(y){
        if(y & 1) res = res*x%mod;
        y >>= 1;
        x = x*x%mod;
    }
    return res;
}
ll primes()
{
    int m = 0;
    for(int i = 2; i <= n; i++){
        if(!v[i]){
            prime[++m] = i;
            v[i] = 1;
            sum[i] = quickpow(i,n);
        }
        for(int j = 1; j <= m; j++){
            if(i*prime[j] > n || i%prime[j] == 0) break;
            v[i*prime[j]] = 1;
            sum[i*prime[j]] = sum[i]*sum[prime[j]]%mod;
        }
    }
    ll ans = 1;
    for(int i = 2; i <= n; i++){
        ans ^= sum[i];
    }
    return ans;
}
int main()
{
    cin>>n;
    printf("%lld\n",primes());
    return 0;
}