input: Write a python function to find the sum of all possible combinations of numbers in a list.
  assert sum_combinations([1, 2, 3, 4]) == 50
  assert sum_combinations([1, 1, 1]) == 10
  assert sum_combinations([2, 5, 7]) == 44
output: def sum_combinations(lst):
      from itertools import combinations
      total_sum = 0
      for r in range(1, len(lst) + 1):
          for combo in combinations(lst, r):
              total_sum += sum(combo)
      return total_sum