#include <fstream>

using namespace std;
ifstream cin ("medie.in");
ofstream cout ("medie.out");
int vc[7005];
int main()
{
    int n, maxi = 0;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        int nr;
        cin >> nr;
        maxi = max(maxi, nr);
        vc[nr]++;
    }
    long long sol = 0;
    for (int i = 1; i <= maxi; i++)
        if (vc[i])
        {
            int j = 2;
            if (i % 2)
                j--;
            while (j < i)
            {
                sol += vc[i] * vc[j] * vc[(i + j) / 2];
                j += 2;
            }
            sol += vc[i] * (vc[i] - 1) * (vc[i] - 2) / 2;
        }
    cout << sol;
    return 0;
}