How to write a statement and an array to individual lines on a text file? Python

a = str(mergeSort(lines))
nlines = ['Sorted Numbers',a]
with open('SortedNumbers.txt', 'w') as f:
    f.writelines(nlines)enter code here

mergeSort(lines) is my array of a few numbers. With this code above, the text file it creates does everything I want except all of it is on one line. How do I get it so the text file it produces will be

Sorted Numbers
1
3
5
8
10

>Solution :

a = "\n".join(mergeSort(lines));

Should put a newline after each of the numbers of your array.

It should print properly afterwards