Tekijät

#include <iostream>
#include <fstream>
#include <vector>
#include <algorithm>
#include <queue>
#include <stack>
#include <set>
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
 
#define F first
#define S second
#define X first
#define Y second
 
const int N = 1e6 + 5;
const ll INF = 1e18;
 
ll am[N];
bool pr[N];
int gpd[N];
 
ll mo[N];
 
void sieve() {
	for(int i = 2; i < N; ++i) {
		pr[i] = true;
	}
	for(ll i = 2; i < N; ++i) {
		if(!pr[i]) continue;
		gpd[i] = i;
		for(ll j = 2*i; j < N; j+=i) {
			gpd[j] = i;
			pr[j] = false;
		}
	}
}
 
 
void add(int x, int d) {
	if(x == 1) {
		++am[d];
		return;
	}
 
	int p = gpd[x];
	int X = x;
	int e = 0;
	while(X%p == 0) {
		++e;
		X/=p;
	}
 
	int c = 1;
	for(int i = 0; i <= e; ++i) {
		add(X, d*c);
		c *= p;
	}
}
 
 
int main() {
	sieve();
 
	mo[1] = 1;
	for(int i = 2; i < N; ++i) {
		ll p = gpd[i];
		if(i%(p*p) == 0) {
			mo[i] = 0;
		} else {
			mo[i] = -mo[i/p];
		}
	}
 
 
	int n;
	cin >> n;
	for(int i = 1; i <= n; ++i) {
		int x;
		cin >> x;
		add(x, 1);
	}
 
 
	ll ans = 0;
	for(int i = 1; i < N; ++i) {
		ans += mo[i] * (am[i] * am[i] - am[i]);
	}
 
	cout << ans/2 << "\n";
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 2, 3

Verdict: ACCEPTED

Test 4

Group: 3

Verdict: ACCEPTED

Test 5

Group: 3

Verdict: ACCEPTED

Test 6

Group: 3

Verdict: ACCEPTED

Test 7

Group: 3

Verdict: ACCEPTED