#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("medie.in");
ofstream fout("medie.out");
const int MAXN = 7005;
unsigned long long sol = 0;
int n, maxx;
int v[MAXN];
int main() {
    fin >> n;
    for (int i = 1; i <= n; ++i) {
        int k;
        fin >> k;
        v[k]++;
        maxx = max(maxx, k);
    }
    for (int i = 1; i <= maxx; ++i) {
        if (v[i] > 2) {
            sol += (1ull) * v[i] * (v[i] - 1) * (v[i] - 2) / 2;
        }
        for (int j = i + 2; j <= maxx; j += 2) {
            int mid = (i + j) / 2;
            unsigned long long s = (1ull) * v[i] * v[j] * v[mid];
            sol += s;
        }
    }
    fout << sol;
    fout.close();
    return 0;
}