luogu 1593 因子和 约数+线性筛

等比数列那里忘判项数等于 $1$ 的情况了.

Code:

#include <cstdio>
#include <vector>
#include <algorithm>
#define mod 9901
#define N 50000002
#define ll long long
#define setIO(s) freopen(s".in","r",stdin)
using namespace std;
ll qpow(ll base,ll k)
{
    ll tmp=1;
    for(;k;base=base*base%mod,k>>=1)if(k&1) tmp=tmp*base%mod;
    return tmp;
}
ll inv(ll k)
{
    return qpow(k,mod-2);
}
ll calc(ll a,ll b,ll k)
{
    if(b==1) return a;
    return (qpow(b,k+1)-1+mod)%mod*inv(b-1)%mod;
}
struct Node
{
    int prime,p;
    Node(int prime=0,int p=0):prime(prime),p(p){}
};
vector<Node>v;
int tot;
bool vis[N];
int prime[4000000];
void init()
{
    int i,j;
    for(i=2;i<N;++i)
    {
        if(!vis[i]) prime[++tot]=i;
        for(j=1;j<=tot&&i*prime[j]<N;++j)
        {
            vis[i*prime[j]]=1;
            if(i%prime[j]==0) break;
        }
    }
}
int main()
{
    init();
    // setIO("input");
    int i,j,AA,B,h;
    scanf("%d%d",&AA,&B),h=AA;
    for(i=1;i<=tot;++i)
        if(h%prime[i]==0)
        {
            int cc=0;
            for(;h%prime[i]==0;h/=prime[i]) ++cc;
            v.push_back(Node(prime[i],cc));
        }
    ll re=1;
    for(i=0;i<v.size();++i)
    {
        int p=v[i].p;
        ll tmp=0,A=1;
        for(j=1;j<=p;++j) A=A*v[i].prime%mod,tmp=(tmp+A)%mod;
        tmp=tmp*calc(1,A,B-1)%mod;
        re=re*(tmp+1)%mod;
    }
    printf("%lld\n",re);
    return 0;
}