tsk 5 (fnc)

def nums(a, b) -> int:
    if a > b:
        return 0
    if a == b:
        return 1
    if a < b:
        return nums(a + 1, b) + nums(a * 2, b)

print(nums(1, 21) - nums(1, 10) * nums(10, 21))