A number sequence is as follows:
5, 100, 6, 200, 7, 400, 8, 800, 9, 1600, 10, 3200, ...
Given that 5 is at position 1, create a function that returns the number found at position n in the sequence.
little_big(4) ➞ 200
little_big(5) ➞ 7
little_big(28) ➞ 819200
You can expect to be only given valid inputs.