#include <iostream>
#include <algorithm>
#define N 100005
using namespace std;

int n;
long long v[32], a[N];

void Generare()
{
    int i;
    long long x;
    x=1;
    for(i=1; i<=30; i++)
        v[i]=x, x*=2;
}

void ReadSort()
{
    ///citire
    cin >> n;
    for(int i=1; i<=n; i++)
        cin >> a[i];
    ///sortez vectorul
    sort(a+1, a+n+1);
}

int CBS(int st, int dr, long long  x)
{
    int m, poz=0;
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(x == v[m])
            poz=m, dr=m-1;
        else if(x<v[m])
                dr=m-1;
        else if(x>v[m])
                st=m+1;
    }
    return poz;
}

int CBD(int st, int dr, long long x)
{
    int m, poz=0;
    while(st<=dr)
    {
        m=(st+dr)/2;
        if(x == v[m])
            poz=m, st=m+1;
        else if(x>=v[m])
                st=m+1;
        else if(x>v[m])
                dr=m-1;
    }
    return poz;
}

int main()
{
    int x, y, ct=0;

    ReadSort();
    ///generam toate puterile lui 2
    Generare();

    ///formam perechi
    for(int i=1; i<n; i++)
        for(int j=1; j<=30; j++)
        {
            x=CBS(i+1, n, v[j]-a[i]);
            y=CBD(i+1, n, v[j]-a[i]);
            ct+= (y-x+1);
        }

    cout << ct;
    return 0;
}