input: Write a function to determine the count of subsequences where the product is less than k for a given array of non-negative integers.
  assert no_of_subsequences([1,2,3,4], 10) == 11
  assert no_of_subsequences([4,8,7,2], 50) == 9
  assert no_of_subsequences([5,6,7,8], 15) == 4
output: def no_of_subsequences(arr, k):
      def count_subsequences(index, prod):
          if index == len(arr):
              return 1 if prod > 0 and prod < k else 0
          if prod >= k:
              return 0
          include = count_subsequences(index + 1, prod * arr[index])
          exclude = count_subsequences(index + 1, prod)
          return include + exclude
      return count_subsequences(0, 1) - 1