1 #include <iostream>
 2 #include <cstdio>
 3 #include <algorithm>
 4 #include <cstring>
 5 #include <vector>
 6 #include <map>
 7 using namespace std;
 8 int n;
 9 long long a[5010],b[5010];
10 int num[5010];
11 template<class T> inline void readint(T& x) {
12       char c;
13       int mul = 1;
14       while((c = getchar()) != EOF){
15          if(c == '-')mul = -1;
16          if(c >= '0' && c <= '9'){
17               x = c-'0';
18               break;
19          }
20       }
21       if(c == EOF){x = EOF;return;}
22       while(c = getchar()){
23           if(c >= '0' && c <= '9'){
24               x = (x<<1)+(x<<3)+(c-'0');
25           }else break;
26       }
27       x *= mul;
28 }
29 int main(){
30     //freopen("in.txt","r",stdin);
31     while(~scanf("%d",&n)){
32         memset(num,0,sizeof num);
33         for(int i=0;i<n;i++) readint(a[i]),b[i]=a[i];
34         sort(a,a+n);
35         sort(b,b+n);
36         int ct=unique(b,b+n)-b;
37         for(int i=0;i<n;i++){
38            int x=lower_bound(b,b+ct,a[i])-b;
39            num[x]++;
40         }
41         long long ans=0;
42         for(int i=0;i<ct;i++){
43            int j=i+1;
44            int x=lower_bound(b,b+ct,2*b[i])-b;
45            if(x<ct&&b[x]==2*b[i]){
46               ans+=num[x]*(long long)num[i]*(num[i]-1)/2;
47            }
48            int k=lower_bound(b,b+ct,b[i]-b[j])-b;
49            for(;j<ct;j++){
50               while(k<ct&&b[i]+b[j]>b[k]) k++;
51               if(k>=ct) continue;
52               if(b[i]+b[j]==b[k]){
53                  ans+=(long long)num[i]*num[j]*num[k];
54               }
55            }
56         }
57         printf("%lld\n",ans);
58     }
59     return 0;
60 }