很明显是莫反。
含因子1的-含因子2的-含因子3的+含因子6的···

#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <iostream>
#include <cmath>
#include <algorithm>
using namespace std;
typedef long long LL;
const int N = 1e4 + 10;
int n, s, p[N], miu[N]; bool v[N];
void get_miu() {
    miu[1] = 1;
    for (int i = 2; i <= 10000; i++) {
        if (!v[i]) p[++s] = i, miu[i] = -1;
        for (int j = 1; j <= s && i * p[j] <= 10000; j++) {
            v[i * p[j]] = 1;
            if (i % p[j] == 0) break;
            miu[i * p[j]] = -miu[i];
        }
    }
}

int sum[N];

LL C(int n, int m) {
    if (n < m) return 0;
    if (!m) return 1;
    double ans = 1.0;
    for (int i = 1; i <= m; i++) ans = 1.0 * ans * (n + 1 - i) / i;
    return (LL)ans;
}

int main() {
    get_miu();
    while (cin >> n) {
        memset(sum, 0, sizeof(sum));
        int m = 0;
        for (int i = 1; i <= n; i++) {
            int x; scanf("%d", &x);
            m = max(m, x);
            for (int j = 1; j * j <= x; j++)
                if (x % j == 0) {
                    sum[j]++;
                    if (j * j != x) sum[x / j]++;
                }
        }
        LL ans = 0;
        for (int i = 1; i <= m; i++)
            ans += 1ll * miu[i] * C(sum[i], 4);
        cout << ans << endl;
    }
    return 0;
}