# Find the sum of the series 1+11+111+1111+….. upto n terms

Here we are going to find the sum of the series 1 + 11 + 111 + 1111 +…..upto N terms (where N is given).

Example :

Input : 3
Output : 1 + 11 + 111 +....
Total sum is : 123

Input : 4
Output : 1 + 11 + 111 + 1111 +.....
Total sum is : 1234

Input : 7
Output : 1 + 11 + 111 + 1111 + 11111 +
111111 + 1111111 +.....
Total sum is : 1234567


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

Here we see that when value of N is 3, series last upto 1 + 11 + 111 i.e, three term and it’s sum is 123.

Program for finding sum of above series :

## C

 // C program to find the sum of  // the series 1+11+111+1111+....  #include     // Function for finding summation  int summation(int n)  {      int sum = 0, j = 1;      for (int i = 1; i <= n; i++) {          sum = sum + j;             // Appending a 1 at the end          j = (j * 10) + 1;      }         return sum;  }     // Driver Code  int main()  {      int n = 5;      printf("%d", summation(n));      return 0;  }

## Java

 // Java program to find the sum of  // the series 1+11+111+1111+....  import java.io.*;     class GFG   {         // Function for finding summation      static int summation(int n)      {          int sum = 0, j = 1;          for (int i = 1; i <= n; i++)           {              sum = sum + j;              j = (j * 10) + 1;          }             return sum;      }         // Driver Code      public static void main(String args[])      {          int n = 5;          System.out.println(summation(n));      }  }     // This code is contributed  // by Nikita Tiwari

## Python

 # Python program to get the summation  # of following series  def summation(n):      sum = 0     j = 1            for i in range(1, n + 1):          sum = sum + j          j = (j * 10) + 1                return sum            # Driver Code  n = 5 print(summation(n))

## C#

 // C# program to find the sum of  // the series 1+11+111+1111+....  using System;     class GFG   {         // Function for finding summation      static int summation(int n)      {          int sum = 0, j = 1;          for (int i = 1; i <= n; i++)           {              sum = sum + j;              j = (j * 10) + 1;          }             return sum;      }         // Driver Code      public static void Main()      {          int n = 5;          Console.WriteLine(summation(n));      }  }     // This code is contributed by vt_m

## PHP

 

Output :

12345


Another method: Let given a series S = 1 + 11 + 111 + 1111 + . . . + upto nth term. Using formula to find sum of series.

Below is the implementation of above approach.

## C++

 // C++ program to find the sum of  // the series 1+11+111+1111+....  #include     // Function for finding summation  int summation(int n)  {      int sum;         sum = (pow(10, n + 1) -                  10 - (9 * n)) / 81;         return sum;  }     // Driver Code  int main()  {      int n = 5;      printf("%d", summation(n));      return 0;  }

## Java

 // java program to find the sum of  // the series 1+11+111+1111+....  import java.io.*;     class GFG {         // Function for finding summation      static int summation(int n)      {          int sum;                 sum = (int)(Math.pow(10, n + 1) -                   10 - (9 * n)) / 81;                 return sum;      }             // Driver Code      public static void main (String[] args)      {          int n = 5;          System.out.println(summation(n));      }  }     // This code is contributed by anuj_67.

## Python3

 # Python3 program to   # find the sum of  # the series 1+11+111+1111+....  import math     # Function for   # finding summation  def summation(n):      return int((pow(10, n + 1) -                      10 - (9 * n)) / 81);     # Driver Code  print(summation(5));     # This code is contributed  # by mits.

## C#

 // C# program to find the sum of  // the series 1+11+111+1111+....  using System;     class GFG {         // Function for finding summation      static int summation(int n)      {          int sum;                 sum = (int)(Math.Pow(10, n + 1) -                   10 - (9 * n)) / 81;                 return sum;      }             // Driver Code      public static void Main ()      {          int n = 5;          Console.WriteLine(summation(n));      }  }     // This code is contributed by anuj_67.

## PHP

 

Output :

12345


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 : surya2106, jit_t, vt_m, Mithun Kumar

Article Tags :
Practice Tags :

Be the First to upvote.

Please write to us at contribute@geeksforgeeks.org to report any issue with the above content.