#include <iostream>
#include <vector>

int count_asakatsu_subsequences(int N, std::vector<int>& A) {
    int cnt = 0;
    for (int i = 0; i < N - 3; i++) {
        for (int j = i + 1; j < N - 2; j++) {
            int k = A[j] - A[i] - 10;
            if (k > 0) {
                for (int m = j + 1; m < N - 1; m++) {
                    if (A[m] == A[j] - k) {
                        for (int n = m + 1; n < N; n++) {
                            if (A[n] == A[m] + k + 1) {
                                cnt += 1;
                            }
                        }
                    }
                }
            }
        }
    }
    return cnt;
}

int main() {
    int N;
    std::cin >> N;
    std::vector<int> A(N);
    for (int i = 0; i < N; i++) {
        std::cin >> A[i];
    }
    int result = count_asakatsu_subsequences(N, A);
    std::cout << result << std::endl;

    return 0;
}