#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

int d[2010][2010];

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  VI a(n);
  rep(i, n) cin >> a[i];
  ll ans = 0;
  rep(i, n) {
    for(int j = i + 1; j < n; j++) {
      int a0 = a[i] - 10;
      int k = a[j] - a0 - 11;
      if (k <= 0) continue;
      int a1 = a0 + k + 10;
      if (1 <= a0 && a1 <= 2000) {
        ans += d[a0][a1];
      }
    }
    rep(k, i) d[a[k]][a[i]]++;
  }
  cout << ans << '\n';
}