Number Sequence

Write a recursive function that accepts an integer n and return a sequence of n integers as a string, descending from n to 1 and then ascending back from 1 to n as in the examples below:

Examples

number_sequence(1) ➞ "1"

number_sequence(2) ➞ "1 1"

number_sequence(3) ➞ "2 1 2"

number_sequence(4) ➞ "2 1 1 2"

number_sequence(9) ➞ "5 4 3 2 1 2 3 4 5"

number_sequence(10) ➞ "5 4 3 2 1 1 2 3 4 5"

Notes

• Only use recursion.
• No auxiliary data structures like list and tuple are allowed.