Tekijät

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

ll c[1010101];

int lol(int x) {
	assert(x>=2);
	int r=0;
	for (int i=2;i*i<=x;i++){
		if (x%i==0){
			r++;
			x/=i;
		}
		if (x%i==0){
			return 0;
		}
	}
	if (x>1) r++;
	if (r%2==1) {
		return 1;
	} else {
		return -1;
	}
}

ll ch(ll x) {
	return x*(x-1ll)/2ll;
}

int main(){
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int n;
	cin>>n;
	for (int i=0;i<n;i++){
		int x;
		cin>>x;
		c[x]++;
	}
	ll ans=0;
	for (int i=2;i<=1000000;i++){
		ll f=0;
		for (int j=i;j<=1000000;j+=i) {
			f+=c[j];
		}
		ans += ch(f)*(ll)lol(i);
	}
	cout<<ch(n)-ans<<endl;
}

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