#include <bits/stdc++.h>
#define ll long long
#define ld long double

using namespace std;

const ll MOD = 1e9 + 7;
const ll INF = 1e9;

ifstream fin ("medie.in");
ofstream fout ("medie.out");


int n, frcv[7002],  mx;

int main()
{
  ios_base::sync_with_stdio(false);
  cin.tie(0); cout.tie(0);
  fin >> n;
  for (int i= 1; i <= n; i++) {
    int x;
    fin >> x;
    mx = max(mx, x);
    frcv[x]++;
  }
  ll ans = 0;
  for (int i = 1; i <= mx; i++) {
    if (frcv[i]) {
      for (int j = i + 2; j <= mx; j += 2) {
        int t = (i + j) / 2;
        ans = ans + 1ll * frcv[i] * frcv[j] * frcv[t];
      }
      ans += 1ll * frcv[i] * (frcv[i] - 1) * (frcv[i] - 2) / 2;
    }
  }
  fout << ans;
  return 0;
}