#define _USE_MATH_DEFINES
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <queue>
#include <math.h>
#include <cmath>
#include <stack>
#include <map>
#include <set>
#include <numeric>
#include <iomanip>
#include <climits>
#include <functional>
#include <cassert>
#include <tuple>
using namespace std;
using ll = long long;

int N;
int A[2020];

int main() {

    cin >> N;
    for(int i = 0; i < N; ++i) cin >> A[i];

    ll ans = 0;
    for(int k = 1; k <= 2000; ++k) {
        vector dp(2001, vector(4,0));
        for(int i = 0; i < N; ++i) {
            int a3 = A[i]-k-1;
            if(a3 > 0 && a3 <= 2000) dp[A[i]][3] += dp[a3][2];
            int a2 = A[i]+k;
            if(a2 > 0 && a2 <= 2000) dp[A[i]][2] += dp[a2][1];
            int a1 = A[i]-k-10;
            if(a1 > 0 && a1 <= 2000) dp[A[i]][1] += dp[a1][0];
            dp[A[i]][0]++;
        }
        for(int i = 1; i <= 2000; ++i) ans += dp[i][3];
    }

    cout << ans << endl;

}