#include <bits/stdc++.h>

using namespace std;
#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 Rep(i,a,b) for (int i = a; i < b; ++i)
#define rRep(i,a,b) for (int i = a; i > b; --i)
#define fore(i,a) for(auto &i:a)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define Unique(v) v.erase(unique(v.begin(), v.end()), v.end());
#define Bit(x,i) (((x)>>(i))&1)
using ll = long long;
using vi = vector<int>;
using vll = vector<long long>;
using vvi = vector<vi>;
using vvll = vector<vll>;
using vb = vector<bool>;
using vs = vector<string>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
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; }
struct settings{settings(){ios_base::sync_with_stdio(0); cin.tie(0); cout<<fixed<<setprecision(15);};}settingss;
const double PI = acos(-1);
const int INF = 1001001001;
const ll LINF = 1001001001001001001LL;

int A[2100];
ll cnt[2100][2100];

int main() {
  int N; cin >> N;
  rep(i, N) cin >> A[i];
  rep(i, N) {
    rep(j, 2001) {
      cnt[i+1][j] += cnt[i][j] + (A[i] == j);
    }
  }
  ll ans = 0;
  Rep(i, 1, N-2) {
    Rep(j, i+1, N-1) {
      int k = A[i] - A[j];
      if(k <= 0) continue;
      int a1 = A[i] - k - 10;
      int a4 = A[j] + k + 1;
      if(a1 < 1 || a1 > 2000 || a4 < 1 || a4 > 2000) continue;
      ll c1 = cnt[i][a1];
      ll c2 = cnt[N][a4] - cnt[j][a4];
      ans += c1 * c2;
    }
  }
  cout << ans << endl;
}