from typing import Dict, List
def main():
n: int = 0
x: int = 0
ans: int = 0
m = dict()
n = int(input().strip())
arr: List[str] = input().strip().split(' ')
arr: List[int] = [*map(int, arr)]
for i in range(0, n):
x = arr[i]
for j in range(0, 31):
key: int = pow(2, j) - x
if key in m:
ans += m[key]
else:
ans += 0
if x not in m:
m[x] = 0
m[x] += 1
print(ans)
main()
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
int main()
{
int n; scanf("%d", &n);
vector<int> a(n + 1);
for (int i = 1; i <= n; i++)
scanf("%d", &a[i]);
ll ans = 0;
for (int j = 1; j <= 30; j++)
{
map<int, int> mp;
for (int i = 1; i <= n; i++)
{
int val = (1 << j);
if (val - a[i] != 0 && mp.count(val - a[i])) ans += mp[val - a[i]];
mp[a[i]]++;
}
}
printf("%lld\n", ans);
return 0;
}
/*
1, 2, 3, 4, 5, 6
*/ 1302. Deepest Leaves Sum | 1209. Remove All Adjacent Duplicates in String II |
994. Rotting Oranges | 983. Minimum Cost For Tickets |
973. K Closest Points to Origin | 969. Pancake Sorting |
967. Numbers With Same Consecutive Differences | 957. Prison Cells After N Days |
946. Validate Stack Sequences | 921. Minimum Add to Make Parentheses Valid |
881. Boats to Save People | 497. Random Point in Non-overlapping Rectangles |
528. Random Pick with Weight | 470. Implement Rand10() Using Rand7() |
866. Prime Palindrome | 1516A - Tit for Tat |
622. Design Circular Queue | 814. Binary Tree Pruning |
791. Custom Sort String | 787. Cheapest Flights Within K Stops |
779. K-th Symbol in Grammar | 701. Insert into a Binary Search Tree |
429. N-ary Tree Level Order Traversal | 739. Daily Temperatures |
647. Palindromic Substrings | 583. Delete Operation for Two Strings |
518. Coin Change 2 | 516. Longest Palindromic Subsequence |
468. Validate IP Address | 450. Delete Node in a BST |