This code defines a function `sum` that calculates the sum...

This code defines a function sum that calculates the sum of elements in a list recursively. The function takes a list list1 as input, initializes a variable sum1 to 0, and then iterates through the indices of the list. If the index i is less than 0, it returns 0. Otherwise, it recursively calculates the sum by calling the sum function on a sublist of list1 up to index i, and adds it to the current sum. The main part of the code takes user input for the size of the list, creates a list of numbers from 0 to n-1, and then prints the sum of the list by calling the sum function on the list.