input: Write a python function that returns the count of subsequences with a product less than k from a given list of non-negative numbers.
  assert count_subsequences([1,2,3,4], 10) == 11
  assert count_subsequences([4,8,7,2], 50) == 9
  assert count_subsequences([5,6,7,8], 15) == 4
output: def count_subsequences(arr, k):
      from itertools import combinations
      count = 0
      n = len(arr)
      for r in range(1, n + 1):
          for subseq in combinations(arr, r):
              product = 1
              for num in subseq:
                  product *= num
                  if product >= k:
                      break
              else:
                  count += 1
      return count