#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using vll =vector<ll>;
using vvll =vector<vll>;
#define rep(i,n) for(ll i=(ll)(0); i<(ll(n)); ++i)
#define all(x) (x).begin(), (x).end()

int main(){
    ll N;
    cin>>N;
    vvll A(2001,vll(N+1));
    vll B(N);
    rep(i,N){
        cin>>B[i];
        A[B[i]][i+1]++;
    }
    rep(i,2001){
        rep(j,N)A[i][j+1]+=A[i][j];
    }

    ll an=0;
    rep(i,N)rep(j,i){
        ll a2=B[j];
        ll a3=B[i];
        ll k=a2-a3;
        if(k<=0)continue;
        ll a1=a2-k-10;
        ll a4=a3+k+1;
        if(a1<=0||a4>=2001)continue;
        ll n1=A[a1][j];
        ll n4=A[a4][N]-A[a4][i];
        an+=n1*n4;
    }
    cout<<an<<endl;
}