# Find M-th number whose repeated sum of digits of a number is N

Given two positive integers N and M. The task is to find M-th number whose sum of digits of a number until sum becomes single digit is N.

Examples:

```Input: N = 1, M = 3
Output: 19
The first two numbers being 1 and 9.

Input: N = 2, M = 5
Output:  38
The first four numbers being 2, 11, 20 and 29.
```

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

A naive approach is to iterate for all numbers and keep a count of number whose sum returns N.

An efficient approach is to find the summation of digits till it becomes single digits in O(1) that has been discussed here. Hence the formula to find M-th number will be:

Mth number: (M-1)*9 + N

Below is the implementation of the above approach:

## C++

 `// C++ program to Find m-th number whose ` `// sum of digits of a number until ` `// sum becomes single digit is N ` `#include ` `using` `namespace` `std; ` ` `  `// Function to find the M-th ` `// number whosesum till one digit is N ` `int` `findNumber(``int` `n, ``int` `m) ` `{ ` `    ``int` `num = (m - 1) * 9 + n; ` `    ``return` `num; ` `} ` ` `  `// Driver Code ` `int` `main() ` `{ ` ` `  `    ``int` `n = 2, m = 5; ` `    ``cout << findNumber(n, m); ` `    ``return` `0; ` `} `

## Java

 `// Java program to Find m-th number whose ` `// sum of digits of a number until ` `// sum becomes single digit is N ` `class` `GFG ` `{ ` ` `  `// Function to find the M-th ` `// number whosesum till one digit is N ` `static` `int` `findNumber(``int` `n, ``int` `m) ` `{ ` `    ``int` `num = (m - ``1``) * ``9` `+ n; ` `    ``return` `num; ` `} ` ` `  `// Driver Code ` `public` `static` `void` `main(String args[]) ` `{ ` `    ``int` `n = ``2``, m = ``5``; ` `    ``System.out.print(findNumber(n, m)); ` `} ` `} ` ` `  `// This code is contributed ` `// by Akanksha Rai `

## Python3

 `# Python3 program to Find m-th number  ` `# whose sum of digits of a number ` `# until sum becomes single digit is N  ` ` `  `# Function to find the M-th  ` `# number whosesum till one digit is N ` `def` `findNumber(n, m) : ` `     `  `    ``num ``=` `(m ``-` `1``) ``*` `9` `+` `n;  ` `    ``return` `num;  ` ` `  `# Driver Code  ` `if` `__name__ ``=``=` `"__main__"` `:  ` ` `  `    ``n ``=` `2` `; ` `    ``m ``=` `5` `;  ` `    ``print``(findNumber(n, m)) ` `     `  `# This code is contributed by Ryuga `

## C#

 `// C# program to Find m-th number whose ` `// sum of digits of a number until ` `// sum becomes single digit is N ` `using` `System; ` ` `  `class` `GFG ` `{ ` ` `  `// Function to find the M-th ` `// number whosesum till one digit is N ` `static` `int` `findNumber(``int` `n, ``int` `m) ` `{ ` `    ``int` `num = (m - 1) * 9 + n; ` `    ``return` `num; ` `} ` ` `  `// Driver Code ` `public` `static` `void` `Main() ` `{ ` `    ``int` `n = 2, m = 5; ` `    ``Console.Write(findNumber(n, m)); ` `} ` `} ` ` `  `// This code is contributed ` `// by Akanksha Rai `

## PHP

 ` `

Output:

```38
``` My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Improved By : Akanksha_Rai, AnkitRai01