BZOJ 4173

我能说我这道题是打表找规律么

并不会证明QAQ.

答案就是phi(n)*phi(n)*n*m

证明去膜拜PoPoQQQ

#pragma GCC optimize ("O3")
#include <iostream>
#include <cstring>
#include <algorithm>
#include <stdio.h>
typedef long long ll;
#define P 998244353ll
ll n,m;
 
 
template<typename _t>
inline _t read(){
    _t x=0,f=1;
    char ch=getchar();
    for(;ch>'9'||ch<'0';ch=getchar())if(ch=='-')f=-f;
    for(;ch>='0'&&ch<='9';ch=getchar())x=x*10+(ch^48);
    return x*f;
}
 
inline ll get_phi(ll x){
    ll ans = 1;
    for(ll i = 2;i*i<=x;i++)
        if(x%i==0){
            ans = ans * (i-1) % P;
            x/=i;
            while(x%i==0){
                ans = ans * i % P;
                x/=i;
            }
        }
    if(x!=1)ans = ans * (x-1) % P;
    return ans;
}
 
int main(){
    n=read<ll>();m=read<ll>();
    ll Ans = (n % P) * (m % P) % P * (get_phi(n) % P) % P * (get_phi(m) % P) % P;
    printf("%lld\n",Ans);
}