#include <bits/stdc++.h>
using namespace std;
int ap[7005];
int main(){
    freopen("medie.in","r",stdin);
    freopen("medie.out","w",stdout);
    int n,Max=-1;
    scanf("%d",&n);
    for(int i=1;i<=n;++i){
        int x;
        scanf("%d",&x);
        ++ap[x];
        if(x>Max) Max=x;
    }
    long long S=0;
    for(int i=1;i<=7000;++i){
        if(ap[i]==0) continue;
        S+=ap[i]*(ap[i]-1)*(ap[i]-2)/2;
        int st=i-1,dr=i+1;
        while(st>=1&&dr<=7000){
            S+=ap[st]*ap[dr]*ap[i];
            --st;
            ++dr;
        }
    }
    printf("%lld\n",S);
    return 0;
}