#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <cmath>
#include <iomanip>
#include <stack>
#include <queue>
#include <numeric>
#include <map>
#include <unordered_map>
#include <set>
#include <fstream>
#include <chrono>
#include <random>
#include <bitset>
//#include <atcoder/all>
#define rep(i,n) for(int i=0;i<(n);i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) ((int)(x).size())
#define pb push_back
using ll = long long;
using namespace std;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
ll gcd(ll a, ll b) {return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) {return a/gcd(a,b)*b;}

int main(){
  int N; cin >> N;
  vector<int> A(N);
  rep(i,N) cin >> A[i];
  ll ans = 0;
  vector<vector<ll>> C(2001,vector<ll>(N+1,0));
  rep(j,2001){
    rep(i,N){
      C[j][i+1] = C[j][i] + (A[i]==j);
    }
  }
  rep(i,N){
    rep(j,i){
      int b = A[j], c = A[i];
      int k = b-c;
      if(k<1) continue;
      int a = A[j]-(10+k);
      int d = A[i]+(k+1);
      if(0<=a && a<=2000 && 0<=d&&d<=2000){
        ans += C[a][j] * (C[d][N]-C[d][i+1]);
      }
    }
  }
  cout << ans << '\n';
  return 0;
};