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

int main() {
    int n; 
    cin >> n;

    set<long>hatvanyok;
    set<long>hasznalt;

    long a = 2;
    for (int i =0; i < 30; i++) {
        hatvanyok.insert(a);
        a = a * 2;
        //cout<<a<< " ";
    }

    //cout<< endl;
    // for (int x : hatvanyok) {
    //     cout<<x<<" ";
    // }
    //cout<<endl;

    vector<int> szamok(n);

    for (int i = 0; i < n; i++) {
        cin >> szamok[i];

    }

    int out = 0;

    for (int i = 0; i < n; i++) {
        for (int j = i+1; j < n; j++) {
            if (!hasznalt.count(szamok[i] + szamok[j])) {
                if (hatvanyok.count(szamok[i] + szamok[j])) {
                    out++;
                    hasznalt.insert(szamok[i] + szamok[j]);
                }
            } else {
                out++;
            }
        }
    }
    cout<<out;
}