# Sum of all odd factors of numbers in the range [l, r]

Given a range [l, r], the task is to find the sum of all the odd factors of the numbers from the given range.

Examples:

Input: l = 6, r = 8
Output: 32
factors(6) = 1, 2, 3, 6, oddfactors(6) = 1, 3 sum_Odd_Factors(6) = 1 + 3 = 4
factors(7) = 1, 7, oddfactors(6) = 1 7, sum_Odd_Factors(7) = 1 + 7 = 8
factors(8) = 1, 2, 4, 8, oddfactors(6) = 1, sum_Odd_Factors(8) = 1 = 1
Therefore sum of all odd factors = 4 + 8 + 1 = 13

Input: l = 1, r = 10
Output: 45

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: We can modify Sieve Of Eratosthenes to store sum of all odd factors of a number at it’s corresponding index. Then we will make a prefix array to store sum upto that index. And now each query can be answered in O(1) using prefix[r] – prefix[l – 1].

Below is the implementation of the above approach:

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` `#define ll long long int ` ` `  `const` `int` `MAX = 100001; ` ` `  `ll prefix[MAX]; ` ` `  `// Function to calculate the prefix sum ` `// of all the odd factors ` `void` `sieve_modified() ` `{ ` `    ``for` `(``int` `i = 1; i < MAX; i += 2) { ` ` `  `        ``// Add i to all the multiples of i ` `        ``for` `(``int` `j = i; j < MAX; j += i) ` `            ``prefix[j] += i; ` `    ``} ` ` `  `    ``// Update the prefix sum ` `    ``for` `(``int` `i = 1; i < MAX; i++) ` `        ``prefix[i] += prefix[i - 1]; ` `} ` ` `  `// Function to return the sum of ` `// all the odd factors of the ` `// numbers in the given range ` `ll sumOddFactors(``int` `L, ``int` `R) ` `{ ` `    ``return` `(prefix[R] - prefix[L - 1]); ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``sieve_modified(); ` `    ``int` `l = 6, r = 10; ` `    ``cout << sumOddFactors(l, r); ` `    ``return` `0; ` `} `

 `// Java implementation of the approach ` `import` `java.io.*; ` ` `  `class` `GFG  ` `{ ` `     `  `static` `int` `MAX = ``100001``; ` `static` `int` `prefix[] = ``new` `int``[MAX]; ` ` `  `// Function to calculate the prefix sum ` `// of all the odd factors ` `static` `void` `sieve_modified() ` `{ ` `    ``for` `(``int` `i = ``1``; i < MAX; i += ``2``)  ` `    ``{ ` ` `  `        ``// Add i to all the multiples of i ` `        ``for` `(``int` `j = i; j < MAX; j += i) ` `            ``prefix[j] += i; ` `    ``} ` ` `  `    ``// Update the prefix sum ` `    ``for` `(``int` `i = ``1``; i < MAX; i++) ` `        ``prefix[i] += prefix[i - ``1``]; ` `} ` ` `  `// Function to return the sum of ` `// all the odd factors of the ` `// numbers in the given range ` `static` `int` `sumOddFactors(``int` `L, ``int` `R) ` `{ ` `    ``return` `(prefix[R] - prefix[L - ``1``]); ` `} ` ` `  `    ``// Driver code ` `    ``public` `static` `void` `main (String[] args) ` `    ``{ ` `        ``sieve_modified(); ` `        ``int` `l = ``6``, r = ``10``; ` `        ``System.out.println (sumOddFactors(l, r)); ` `    ``} ` `} ` ` `  `// This code is contributed by jit_t `

 `# Python3 implementation of the approach ` `MAX` `=` `100001``; ` ` `  `prefix ``=` `[``0``] ``*` `MAX``; ` ` `  `# Function to calculate the prefix sum ` `# of all the odd factors ` `def` `sieve_modified(): ` ` `  `    ``for` `i ``in` `range``(``1``, ``MAX``, ``2``): ` ` `  `        ``# Add i to all the multiples of i ` `        ``for` `j ``in` `range``(i, ``MAX``, i): ` `            ``prefix[j] ``+``=` `i; ` ` `  `    ``# Update the prefix sum ` `    ``for` `i ``in` `range``(``1``, ``MAX``): ` `        ``prefix[i] ``+``=` `prefix[i ``-` `1``]; ` ` `  `# Function to return the sum of ` `# all the odd factors of the ` `# numbers in the given range ` `def` `sumOddFactors(L, R): ` ` `  `    ``return` `(prefix[R] ``-` `prefix[L ``-` `1``]); ` ` `  `# Driver code ` `sieve_modified(); ` `l ``=` `6``; ` `r ``=` `10``; ` `print``(sumOddFactors(l, r)); ` ` `  `# this code is contributed by chandan_jnu `

 `// C# implementation of the approach  ` `using` `System; ` ` `  `class` `GFG ` `{ ` ` `  `public` `static` `int` `MAX = 100001; ` `public` `static` `int``[] prefix = ``new` `int``[MAX]; ` ` `  `// Function to calculate the prefix sum  ` `// of all the odd factors  ` `public` `static` `void` `sieve_modified() ` `{ ` `    ``for` `(``int` `i = 1; i < MAX; i += 2) ` `    ``{ ` ` `  `        ``// Add i to all the multiples of i  ` `        ``for` `(``int` `j = i; j < MAX; j += i) ` `        ``{ ` `            ``prefix[j] += i; ` `        ``} ` `    ``} ` ` `  `    ``// Update the prefix sum  ` `    ``for` `(``int` `i = 1; i < MAX; i++) ` `    ``{ ` `        ``prefix[i] += prefix[i - 1]; ` `    ``} ` `} ` ` `  `// Function to return the sum of  ` `// all the odd factors of the  ` `// numbers in the given range  ` `public` `static` `int` `sumOddFactors(``int` `L, ``int` `R) ` `{ ` `    ``return` `(prefix[R] - prefix[L - 1]); ` `} ` ` `  `// Driver code  ` `public` `static` `void` `Main(``string``[] args) ` `{ ` `    ``sieve_modified(); ` `    ``int` `l = 6, r = 10; ` `    ``Console.WriteLine(sumOddFactors(l, r)); ` `} ` `} ` ` `  `// This code is contributed by Shrikant13 `

 ` `

Output:
```32
```

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Improved By : jit_t, shrikanth13, Chandan_Kumar

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