LibreOJ 6053 简单的函数

注意到质数除了 2 都是奇数，故 f(p)=p−1+2[p=2]。

于是有 G0,0(n)=−n+1,G0,1=(n+2)(n−1)2。
然后对 2 讨论一下即可。

代码：

#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
const long long N = 1e10;
const int MX = 1e5;
const int mod = 1e9 + 7;
const int inv = 5e8 + 4;
long long n;
int lim;
int vis[MX + 5],prime[MX + 5],cnt,Gprime[MX + 5];
int tot,le[MX + 5],ge[MX + 5];
long long lis[2 * MX + 5];
int G[2 * MX + 5][2],Fprime[2 * MX + 5];
inline int &id(long long x)
{
    return x <= lim ? le[x] : ge[n / x];
}
int F(int k,long long n)
{
    if(n < prime[k] || n <= 1)
        return 0;
    int ret = (Fprime[id(n)] - (Gprime[k - 1] - (k - 1) + mod) % mod + mod) % mod;
    if(k == 1)
        ret += 2;
    for(register int i = k;i <= cnt && (long long)prime[i] * prime[i] <= n;++i)
    {
        long long pw = prime[i],pw2 = (long long)prime[i] * prime[i];
        for(register int c = 1;pw2 <= n;++c,pw = pw2,pw2 *= prime[i])
            ret = (ret + (long long)(prime[i] ^ c) * F(i + 1,n / pw) % mod + (prime[i] ^ c + 1)) % mod;
    }
    return ret;
}
int main()
{
    for(register int i = 2;i <= MX;++i)
    {
        if(!vis[i])
            prime[++cnt] = i,Gprime[cnt] = (Gprime[cnt - 1] + i) % mod;
        for(register int j = 1;j <= cnt && i * prime[j] <= MX;++j)
        {
            vis[i * prime[j]] = 1;
            if(!(i % prime[j]))
                break;
        }
    }
    scanf("%lld",&n),lim = sqrt(n);
    for(register long long l = 1,r;l <= n;l = r + 1)
    {
        r = n / (n / l);
        lis[id(n / l) = ++tot] = n / l;
        G[tot][0] = (n / l % mod - 1 + mod) % mod,G[tot][1] = (n / l % mod + 2) * (n / l % mod - 1 + mod) % mod * inv % mod;
    }
    for(register int k = 1;k <= cnt;++k)
    {
        int p = prime[k];
        long long s = (long long)p * p;
        for(register int i = 1;lis[i] >= s;++i)
            G[i][0] = (G[i][0] - (G[id(lis[i] / p)][0] - (k - 1) + mod) % mod + mod) % mod,
            G[i][1] = (G[i][1] - (long long)p * ((G[id(lis[i] / p)][1] - Gprime[k - 1] + mod) % mod) % mod + mod) % mod;
    }
    for(register int i = 1;i <= tot;++i)
        Fprime[i] = (G[i][1] - G[i][0] + mod) % mod;
    printf("%d\n",(F(1,n) + 1) % mod);
}