#include <bits/stdc++.h>
using namespace std;
const long long OO = 1LL << 60;
const long double dOO = (double)INT_MAX;
long long mod = 1000000007;
long double eps = 1e-6;
long long a[100009];
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    long long x;
    scanf("%I64d", &x);
    a[i] = x;
  }
  sort(a, a + n);
  long long ans = 0;
  for (int i = 0; i < n; i++) {
    for (long long m = 1; m <= 2000000000LL; m <<= 1) {
      long long u = upper_bound(a + i + 1, a + n, m - a[i]) - a;
      long long l = lower_bound(a + i + 1, a + n, m - a[i]) - a;
      ans += u - l;
      if (l == n) break;
    }
  }
  printf("%I64d\n", ans);
  return 0;
}
