Question
Find sum of divisors till n
You're given a positive integer N. The task is to find the value of Σi from 1 to N F(i) where function F(i) for the number i is defined as the sum of all divisors of i.
Input
You are given an integer n ( 1<= n <= 106).
Output
Output an integer.
Example
Input:
4
Output:
15
Explanation:
F(1) = 1
F(2) = 1 + 2 = 3
F(3) = 1 + 3 = 4
F(4) = 1 + 2 + 4 = 7
ans = F(1) + F(2) + F(3) + F(4)
= 1 + 3 + 4 + 7
= 15
4
Output:
15
Explanation:
F(1) = 1
F(2) = 1 + 2 = 3
F(3) = 1 + 3 = 4
F(4) = 1 + 2 + 4 = 7
ans = F(1) + F(2) + F(3) + F(4)
= 1 + 3 + 4 + 7
= 15