#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
#define int long long
#define intu __int128_t
#define rep(i,n) for(int i=0;i<n;++i)
#define rep1(i,n) for(int i=1;i<=n;++i)
#define reps(i,a,b,c) for(int i=a;i<b;i+=c)
#define repnega(i,a,b) for(int i=b;i>a;i--)
#define mod2 1000000007
#define mod 998244353
#define endl '\n'
#define AC ios_base::sync_with_stdio(false);cin.tie(0);
#define pb push_back
#define eb emplace_back
#define ceil(a,b) (a+b-1)/b
// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")

int n;
signed main(){
    cin>>n;
    vector<int> a(n);
    set<int> st;
    rep(i,n)cin>>a[i];
    rep(i,n)st.insert(a[i]);
    int ans=0;
    rep1(k,2000){
        map<int,tuple<int,int,int,int>> mp;
        rep(i,n){
            get<0>(mp[a[i]])++;
            get<1>(mp[a[i]])+=get<0>(mp[a[i]-k-10]);
            get<2>(mp[a[i]])+=get<1>(mp[a[i]+k]);
            get<3>(mp[a[i]])+=get<2>(mp[a[i]-k-1]);
        }
        for(auto e:mp){
            ans+=(int)get<3>(e.second);
        }
    }
    cout<<ans<<endl;
    
}