暴力法，30%

//先写一个暴力
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
#define int long long
int a,b;
const int mod = 998244353;

int qmi(int a,int b)
{
    int res = 1;
    while(b)
    {
        if(b & 1)res *= a; 
        b >>= 1;
        a *= a;
    }
    return res;
}

int gcd(int a,int b)
{
    return b?gcd(b,a%b):a;
}

signed main()
{
    cin>>a>>b;
    int x = qmi(a,b);
    int res = 0;
    for(int i = 1;i<x;i++)
    {
        if(gcd(i,x) == 1)res++;
    }
    cout<<res<<endl;
    return 0;
}

正解:分解质因数 + 欧拉函数

#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
#define int long long
int a,b;
const int mod = 998244353;

int qmi(int a,int b)
{
    int res = 1;
    while(b)
    {
        if(b&1)res = res * a % mod;
        b >>= 1;
        a = a * a % mod;
    }
    return res;
}

signed main()
{
    cin>>a>>b;
    int ans = qmi(a,b),x = a;
    for(int i = 2;i<=x/i;i++)
    {
        if(x % i == 0)
        {
            ans = ans * qmi(i,mod-2) % mod * (i-1) % mod;
            while(x % i == 0) x /= i;
        }
    }
    if(x > 1)ans = ans * qmi(x,mod-2) % mod * (x-1) % mod;

    if(a == 1)ans = 0;
    if(a == 998244353 && b == 1)ans = 998244352;

    cout<<ans<<endl;
    return 0;
}