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# Self Numbers

• Last Updated : 01 Aug, 2021

A Number N is said to be Self Number if it can not be written as M + sum of digits of M for any M.
The first few Self numbers are:

1, 3, 5, 7, 9, 20, 31, 42…………….

### Check if N is a Self number

Given an integer N, the task is to find if this number is Self number or not.
Examples:

Input: N = 3
Output: Yes
Explanation:
1 + sumofDigits(1) = 2
2 + sumofDigits(2) = 4
3 + sumofDigits(3) = 6
Hence 3 can not be written as
m + sum of digits of m for any m.
Input: N = 4
Output: No
2 + sumodDigits(2) = 4

Approach: The idea is to iterate from 1 to N and for each number check that sum of its value and sum of its digit is equal to N or not. If yes then the number is not a self number. Otherwise, the number is a self number.
For Example:

if N = 3
// Check for every number
// from 1 to N
1 + sumofDigits(1) = 1
2 + sumofDigits(2) = 4
3 + sumofDigits(3) = 6
Hence 3 can not be written as
M + sum of digits of M for any M.

Below is the implementation of the above approach:

Example :

## C++

 `// C++ implementation to check if the``// number is a self number or not` `#include ``using` `namespace` `std;` `// Function to find the sum of``// digits of a number N``int` `getSum(``int` `n)``{``    ``int` `sum = 0;``    ``while` `(n != 0) {``        ``sum = sum + n % 10;``        ``n = n / 10;``    ``}``    ``return` `sum;``}` `// Function to check for Self number``bool` `isSelfNum(``int` `n)``{``    ``for` `(``int` `m = 1; m <= n; m++) {``        ``if` `(m + getSum(m) == n)``            ``return` `false``;``    ``}``    ``return` `true``;``}` `// Driver code``int` `main()``{``    ``int` `n = 20;` `    ``if` `(isSelfNum(n)) {``        ``cout << ``"Yes"``;``    ``}``    ``else` `{``        ``cout << ``"No"``;``    ``}``    ``return` `0;``}`

## Java

 `// Java implementation to check if the``// number is a self number or not``class` `GFG{``    ` `// Function to find the sum``// of digits of a number N``static` `int` `getSum(``int` `n)``{``    ``int` `sum = ``0``;``    ``while` `(n != ``0``)``    ``{``        ``sum = sum + n % ``10``;``        ``n = n / ``10``;``    ``}``    ``return` `sum;``}` `// Function to check for Self number``static` `boolean` `isSelfNum(``int` `n)``{``    ``for``(``int` `m = ``1``; m <= n; m++)``    ``{``       ``if` `(m + getSum(m) == n)``           ``return` `false``;``    ``}``    ``return` `true``;``}` `// Driver code``public` `static` `void` `main(String[] args)``{``    ``int` `n = ``20``;` `    ``if` `(isSelfNum(n))``    ``{``        ``System.out.println(``"Yes"``);``    ``}``    ``else``    ``{``        ``System.out.println(``"No"``);``    ``}``}``}` `// This code is contributed by Ritik Bansal`

## Python3

 `# Python3 implementation to check if the``# number is a self number or not` `# Function to find the sum of``# digits of a number N``def` `getSum(n):` `    ``sum1 ``=` `0``;``    ``while` `(n !``=` `0``):``        ``sum1 ``=` `sum1 ``+` `n ``%` `10``;``        ``n ``=` `n ``/``/` `10``;``    ` `    ``return` `sum1;` `# Function to check for Self number``def` `isSelfNum(n):` `    ``for` `m ``in` `range``(``1``, n ``+` `1``):``        ``if` `(m ``+` `getSum(m) ``=``=` `n):``            ``return` `False``;``    ` `    ``return` `True``;` `# Driver code``n ``=` `20``;` `if` `(isSelfNum(n)):``    ``print``(``"Yes"``);` `else``:``    ``print``(``"No"``);` `# This code is contributed by Code_Mech`

## C#

 `// C# implementation to check if the``// number is a self number or not``using` `System;``class` `GFG{``    ` `// Function to find the sum``// of digits of a number N``static` `int` `getSum(``int` `n)``{``    ``int` `sum = 0;``    ``while` `(n != 0)``    ``{``        ``sum = sum + n % 10;``        ``n = n / 10;``    ``}``    ``return` `sum;``}` `// Function to check for Self number``static` `bool` `isSelfNum(``int` `n)``{``    ``for``(``int` `m = 1; m <= n; m++)``    ``{``       ``if` `(m + getSum(m) == n)``           ``return` `false``;``    ``}``    ``return` `true``;``}` `// Driver code``public` `static` `void` `Main()``{``    ``int` `n = 20;` `    ``if` `(isSelfNum(n))``    ``{``        ``Console.Write(``"Yes"``);``    ``}``    ``else``    ``{``        ``Console.Write(``"No"``);``    ``}``}``}` `// This code is contributed by Code_Mech`

## Javascript

 ``
Output:
`Yes`

Time Complexity: O(log10N)

Auxiliary Space: O(1)

References: https://en.wikipedia.org/wiki/Self_number

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