#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;

typedef modint998244353 mint;
typedef long long ll;

#define rep(i, s, n) for (int i = (int)(s); i < (int)(n); i++)
#define rrep(i, s, n) for (int i = (int)(n)-1; i >= (int)(s); i--)

template <typename T> bool chmin(T &a, const T &b) {
	if (a <= b) return false;
	a = b;
	return true;
}
template <typename T> bool chmax(T &a, const T &b) {
	if (a >= b) return false;
	a = b;
	return true;
}

int main(){
	int n; cin >> n;
	vector<int> a(n);
	rep(i,0,n) cin >> a[i];
	ll ans = 0;
	rep(k,1,2001){
		vector<ll> dp0(2001);
		vector<ll> dp1(2001);
		vector<ll> dp2(2001);
		vector<ll> dp3(2001);
		rep(i,0,n){
			// 3
			if (a[i]-k-1 >= 0) dp3[a[i]] += dp2[a[i]-k-1];
			// 2
			if (a[i]+k <= 2000) dp2[a[i]] += dp1[a[i]+k];
			// 1
			if (a[i]-k-10 >= 0) dp1[a[i]] += dp0[a[i]-k-10];
			// 0
			dp0[a[i]] += 1;
		}
		rep(i,0,2001){
			ans += dp3[i];
		}
	}
	cout << ans << endl;
}