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Cod sursa(job #917962)
#include <cstdio>
#include <vector>
using namespace std;
#define max_val 1000005
#define max_n 100005
#define FORIT( it,v ) for(typeof((v).begin()) it=(v).begin(); it!=(v).end(); ++it )
vector<int> Div[max_val];
bool Viz[max_val];
int Ap[max_val],El[max_n];
int n,i,j,c,nr,ind,rez,act;
int main(){
freopen("pairs.in","r",stdin);
freopen("pairs.out","w",stdout);
scanf("%d", &n );
for( i=1; i<=n; ++i ){
scanf("%d", &El[i] );
}
for( i=2; i<max_val; ++i ){
if( !Viz[i] ){
for( j=i; j<max_val; j+=i ){
Div[j].push_back(i);
Viz[j]=1;
}
}
}
for( i=1; i<=n; ++i ){
for( j=1; j< (1<<Div[ El[i] ].size() ); ++j ){
nr=1;
for( c=0; c<Div[ El[i] ].size(); ++c ){
if( (1<<c)&j )
nr*=Div[ El[i] ][c];
}
Ap[nr]++;
}
}
for( i=1; i<=n; ++i ){
act=0;
for( j=1; j< (1<<Div[ El[i] ].size()); ++j ){
ind=0;
nr=1;
for( c=0; c<Div[ El[i] ].size(); ++c ){
if( (1<<c)&j ){
ind++;
nr*=Div[ El[i] ][c];
}
}
if( (ind&1) )
act+=Ap[nr];
else
act-=Ap[nr];
}
rez+=n-act;
}
printf("%d\n",rez/2);
return 0;
}