#include <bits/stdc++.h>
using namespace std;
ifstream fin("medie.in");
ofstream fout("medie.out");
int n, mx, fr[7005];
long long ans;
int main()
{
    fin >> n;
    for (int i = 1; i <= n; ++i)
    {
        int x;
        fin >> x;
        fr[x]++;
        mx = max(mx, x);
    }
    for (int i = 1; i <= mx; ++i)
    {
        int j = 1;
        if (i % 2 == 0) j = 2;
        while (j < i)
        {
            ans += fr[i] * fr[j] * fr[(i + j) / 2];
            j += 2;
        }
        ans += (fr[i] - 2) * (fr[i] - 1) * fr[i] / 2;
    }
    fout << ans;
    fin.close();
    fout.close();
    return 0;
}