CF——Codeforces Round #428 (Div. 2)D. Winter is here

D. Winter is here

#include<bits/stdc++.h>
#define maxn 1000000 + 10
const int  MOD =  1000000000 + 7;
typedef long long LL;

using namespace std;
LL ans=0;
LL cnt[maxn];
LL a[maxn];
LL p[maxn];
void init()
{
LL k = 1;
p[0] = 1;
for(int i = 1; i < maxn; i++)
{
p[i] = (p[i-1]*2);
p[i] = p[i] % MOD;
}
//  cout << p[0] << " " << p[1] << " " << p[2] << endl;
}
LL GCD(LL a,LL b)
{
if(b == 0) return a;
else return GCD(b,a%b);
}
int main()
{
int n;
cin >> n;
init();
memset(a,0,sizeof(a));
memset(cnt,0,sizeof(cnt));
for(int i = 0; i < n; i++)
{
int e;
scanf("%I64d",&e);
a[e]++;
if(e>1) ans += e;
ans %= MOD;
}
for(int i = 2; i <= 1000000; i++)
{
for(int j = i; j <= 1000000;j+=i)
{
cnt[i] += a[j];
}
//  if(cnt[i]) cout << cnt[i] << " " << p[cnt[i]-1] << endl;
if(cnt[i])
cnt[i] = (p[cnt[i]-1]-1)*cnt[i]%MOD;
//  if(cnt[i]) cout << i << " " << cnt[i] << endl;
}
for(int i = 1000000; i >= 2; i--)
{
if(cnt[i] == 0) continue;
for(int j = 2*i; j <= 1000000; j+=i)
{
cnt[i] -= cnt[j];
cnt[i] = (cnt[i] + MOD)%MOD;
}
ans += cnt[i]*i;
ans %= MOD;
}
cout << ans%MOD << endl;
return 0;
}