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# C Program for Find sum of odd factors of a number

• Last Updated : 30 Mar, 2021

Given a number n, the task is to find the odd factor sum.
Examples:

```Input : n = 30
Output : 24
Odd dividers sum 1 + 3 + 5 + 15 = 24

Input : 18
Output : 13
Odd dividers sum 1 + 3 + 9 = 13```

Let p1, p2, … pk be prime factors of n. Let a1, a2, .. ak be highest powers of p1, p2, .. pk respectively that divide n, i.e., we can write n as n = (p1a1)*(p2a2)* … (pkak).

```Sum of divisors = (1 + p1 + p12 ... p1a1) *
(1 + p2 + p22 ... p2a2) *
.............................................
(1 + pk + pk2 ... pkak) ```

To find sum of odd factors, we simply need to ignore even factors and their powers. For example, consider n = 18. It can be written as 2132 and sun of all factors is (1)*(1 + 2)*(1 + 3 + 32). Sum of odd factors (1)*(1+3+32) = 13.
To remove all even factors, we repeatedly divide n while it is divisible by 2. After this step, we only get odd factors. Note that 2 is the only even prime.

## C++

 `// Formula based CPP program``// to find sum of all``// divisors of n.``#include ``using` `namespace` `std;` `// Returns sum of all factors of n.``int` `sumofoddFactors(``int` `n)``{``    ``// Traversing through all``    ``// prime factors.``    ``int` `res = 1;` `    ``// ignore even factors by``    ``// removing all powers of``    ``// 2``    ``while` `(n % 2 == 0)``        ``n = n / 2;` `    ``for` `(``int` `i = 3; i <= ``sqrt``(n); i++)``    ``{` `        ``// While i divides n, print``        ``// i and divide n``        ``int` `count = 0, curr_sum = 1``        ``int` `curr_term = 1;``        ``while` `(n % i == 0) {``            ``count++;` `            ``n = n / i;` `            ``curr_term *= i;``            ``curr_sum += curr_term;``        ``}` `        ``res *= curr_sum;``    ``}` `    ``// This condition is to handle``    ``// the case when n is a prime``    ``// number.``    ``if` `(n >= 2)``        ``res *= (1 + n);` `    ``return` `res;``}` `// Driver code``int` `main()``{``    ``int` `n = 30;``    ``cout << sumofoddFactors(n);``    ``return` `0;``}`

## Java

 `// Formula based Java program``// to find sum of all``// divisors of n.``import` `java.io.*;` `class` `GFG``{``    ``// Returns sum of all factors of n.``    ``static` `int` `sumofoddFactors(``int` `n)``    ``{``        ``// Traversing through all``        ``// prime factors.``        ``int` `res = ``1``;``    ` `        ``// ignore even factors by``        ``// removing all powers of``        ``// 2``        ``while` `(n % ``2` `== ``0``)``            ``n = n / ``2``;``    ` `        ``for` `(``int` `i = ``3``; i <= Math. sqrt(n); i++)``        ``{``    ` `            ``// While i divides n, print``            ``// i and divide n``            ``int` `count = ``0``, curr_sum = ``1``;``            ``int` `curr_term = ``1``;``            ``while` `(n % i == ``0``)``            ``{``                ``count++;``    ` `                ``n = n / i;``    ` `                ``curr_term *= i;``                ``curr_sum += curr_term;``            ``}``    ` `            ``res *= curr_sum;``        ``}``    ` `        ``// This condition is to handle``        ``// the case when n is a prime``        ``// number.``        ``if` `(n >= ``2``)``            ``res *= (``1` `+ n);``    ` `        ``return` `res;``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `main (String[] args) {``        ``int` `n = ``30``;``        ``System.out.println ( sumofoddFactors(n));``    ``}``}` `// This code is contributed by vt_m.`

## Python 3

 `# Formula based Python 3 program``# to find sum of all  divisors of n` `# Returns sum of all factors of n``import` `math``def` `sumofoddFactors(n):` `    ``# Traversing through all prime factors``    ``res ``=` `1` `    ``# ignore even factors by``    ``# removing all powers of 2``   ` `    ``while` `(n ``%` `2``) ``=``=` `0` `:``        ``n ``=` `n ``/` `2``    ``i``=``3``    ``while` `i <``=` `math.sqrt(n):``    ` `        ``# While i divides n, print``        ``# i and divide n``        ``count ``=` `0``        ``curr_sum ``=` `1``        ``curr_term ``=` `1``        ``while` `(n ``%` `i) ``=``=` `0``:``            ``count ``+``=` `1``            ``n ``=` `n ``/` `i``            ``curr_term ``*``=` `i``            ``curr_sum ``+``=` `curr_term``        ``res ``*``=` `curr_sum``    ` `    ``# This condition is to handle``    ``# the case when n is a prime number.``    ``if` `(n >``=` `2``):``        ``res ``*``=` `(``1` `+` `n)`` ` `    ``return` `res`` ` `# Driver code``n ``=` `30``print``(``int``(sumofoddFactors(n)))` `# This code is contributed``# by Azkia Anam.`

## C#

 `// Formula based Java program``// to find sum of all``// divisors of n.``using` `System;` `class` `GFG``{``    ``// Returns sum of all factors of n.``    ``static` `int` `sumofoddFactors(``int` `n)``    ``{``        ``// Traversing through all``        ``// prime factors.``        ``int` `res = 1;``    ` `        ``// ignore even factors by``        ``// removing all powers of``        ``// 2``        ``while` `(n % 2 == 0)``            ``n = n / 2;``    ` `        ``for` `(``int` `i = 3; i <= Math. Sqrt(n); i++)``        ``{``    ` `            ``// While i divides n, print``            ``// i and divide n``            ``int` `count = 0, curr_sum = 1;``            ``int` `curr_term = 1;``            ``while` `(n % i == 0)``            ``{``                ``count++;``    ` `                ``n = n / i;``    ` `                ``curr_term *= i;``                ``curr_sum += curr_term;``            ``}``    ` `            ``res *= curr_sum;``        ``}``    ` `        ``// This condition is to handle``        ``// the case when n is a prime``        ``// number.``        ``if` `(n >= 2)``            ``res *= (1 + n);``    ` `        ``return` `res;``    ``}``    ` `    ``// Driver code``    ``public` `static` `void` `Main ()``    ``{``        ``int` `n = 30;``        ``Console.WriteLine( sumofoddFactors(n));``    ``}``}` `// This code is contributed by vt_m.`

## PHP

 `= 2)``        ``\$res` `*= (1 + ``\$n``);` `    ``return` `\$res``;``}` `// Driver code``\$n` `= 30;``echo` `sumofoddFactors(``\$n``);` `// This code is contributed``// by Sach_Code``?>`

Output:

`24`

Time Complexity: O(n1/2)

Auxiliary Space: O(1)
Please refer complete article on Find sum of odd factors of a number for more details!

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