欧拉筛 + 欧拉函数

/**
 *  Fuck you.
 *  I love you too.
 */
#include
#define lson i<<2
#define rson i<<2|1
#define LS l,mid,lson
#define RS mid+1,r,rson
#define mem(a,x) memset(a,x,sizeof(a))
#define gcd(a,b) __gcd(a,b)
#define ll long long
#define ull unsigned long long
#define lowbit(x) (x&-x)

const int INF = 0x3f3f3f3f;
const int EXP = 1e-8;
const int n = 1e5 + 5;
const int MOD = 1e9 + 7;
const int MAXN = 1e5 + 5;

using namespace std;

bool notprime[MAXN];    //是否为素数
int prime[MAXN];        //素数表
int phi[MAXN];          //欧拉函数表

void euler_sieve () {
    int tot = 0;
    mem (notprime, 0);
    for (int i = 2; i < MAXN; ++i) {
        if (!notprime[i]) {
            prime[tot++] = i, phi[i] = i - 1;
        }
        for (int j = 0; j < tot; ++j) {
            if (i * prime[j] > MAXN) {
                break;
            }
            notprime[i * prime[j]] = 1;
            if (i % prime[j] == 0) {
                phi[i * prime[j]] = phi[i] * prime[j];
                break;
            } else {
                phi[i * prime[j]] = phi[i] * (prime[j] - 1);
            }
        }
    }
}

int main() {
    euler_sieve();
    for (int i = 2; i <= 10; i++) {
        cout << phi[i] << endl;
    }
    return 0;
}