Shashank and List Attempt

#include <iostream>
#include <vector>
#include <cmath>
using namespace std;

vector<int> getExponents(vector<int> arr) {
    std::vector<int> ret;
    std::vector<int> group; // indexes to be added
    group.reserve(arr.size());

    for (int length=1; length <= arr.size(); ++length) {
        group.resize(length);

        for (int i=0; i < group.size(); ++i) { // initialize group
            group[i] = i;
        }

        bool stop = false;
        while (!stop)  {// until list is exhausted
            // add sum ()
            ret.push_back(0);
            for (int i=0; i < group.size(); ++i) {
                ret.back() += arr[group[i]];
            }

            // iterate group
            group.back()++; // increase back
            if (group.back() >= arr.size()) { // if back index points too far
                // move first index up and re-init
                group[0]++;

                if (group[0] >= arr.size()) // if first index is invalid, goto length loop (b/c size should be 1)
                    break;

                // re-init
                for (int n=1; n < group.size(); ++n) { // adjust past first
                    group[n] = group[n-1] + 1;

                    if (group[n] >= arr.size()) { // if index is invalid (size is too big), goto length loop (b/c group.size() may be < arr.size())
                        stop = true;
                        break;
                    }
                }
            }
        }
    }

    return ret;
}

int main () {
    unsigned T;
    cin >> T;

    vector<int> arr;
    arr.resize(T);

    for (int i=0; i < T; ++i)
        cin >> arr[i];

    vector<int> exponents = getExponents(arr);

    int sum =0;
    for (int& n : exponents) {
        sum += fmod(exp2(n), (pow(10,9) + 7));
    }

    std::cout << sum;
}