Java Program to Find the Sum of Series (1*2) + (2*3) + (3*4) + …… + N

Java Program to Find the Sum of Series (1*2) + (2*3) + (3*4) + …… + N

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In the previous article, we have discussed about Java Program to Print Series 9 18 27 36 45 54 …N

In this article we are going to see how to find the sum of the series (1*2) + (2*3) + (3*4) + …… + N by using java programming language.

Java Program to Find the Sum of Series (1*2) + (2*3) + (3*4) + …… + N

On observing the pattern carefully, we can see each term is like (a*b) format. Value of ‘a‘ starts from 1 and ‘b‘ value is like ‘a+1‘ and in next term of series previous ‘b‘ value is the value of ‘a‘

Example:

N = 5

1*2 + 2*3 + 3*4 + 4*5 + 5*6 = 2+6+12+20+30 = 70

Let’s see different ways to find the sum of the series (1*2) + (2*3) + (3*4) + …… + N

Method-1: Java Program to Find the Sum of Series (1*2) + (2*3) + (3*4) + …… + N By Using For Loop

Approach:

  • Create Scanner class object.
  • Declare an integer variable say ‘n’ which holds the value of number of terms in series.
  • Declare an integer variable say ‘sum‘ and initialize it to 0.
  • Prompt the user to enter a number as value of n.
  • Use a for loop from i=1 to i<=n
  • Inside for loop we will multiply i*(i+1) and add with sum.
  • Print the result.

Program:

import java.util.*;
public class Main
{
    public static void main(String args[])
    {
        //creating object of Scanner class 
        Scanner s = new Scanner(System.in);
        //Taking input of number of elements in the series
        System.out.println("Enter the value of last number 'n' ");
        int n = s.nextInt();
        //for loop to print the series
        int sum = 0;
        for (int i = 1; i <= n; i++)
            sum += i * (i + 1);
        System.out.println("Sum of the series is " + sum);
    }
}

Output:

Enter the value of last number 'n' 
5
Sum of the series is 70

Method-2: Java Program to Find the Sum of Series (1*2) + (2*3) + (3*4) + …… + N By Using While Loop

Approach:

  • Create Scanner class object.
  • Declare an integer variable say ‘n’ which holds the value of number of terms in series.
  • Declare an integer variable say ‘sum‘ and initialize it to 0.
  • Prompt the user to enter a number as value of n.
  • Use a while loop from i=1 till i<=n
  • Inside while loop we will multiply i*(i+1) and add with sum.
  • Print the result.

Program:

import java.util.*;
public class Main
{
    public static void main(String args[])
    {
        //creating object of Scanner class 
        Scanner s = new Scanner(System.in);
        //Taking input of number of elements in the series
         System.out.println("Enter the value of last number 'n' ");
        int n = s.nextInt();
        // while loop to print the series
        int sum = 0;
        int i = 1;
        while(i <= n)
        {
            sum += i * (i + 1);
             i++;
        }
        System.out.println("Sum of the series is " + sum);
    }
}

Output:

Enter the value of last number 'n' 
9
Sum of the series is 330

Method-3: Java Program to Find the Sum of Series (1*2) + (2*3) + (3*4) + …… + N By Using User Defined Method

Approach:

  • Create Scanner class object.
  • Declare an integer variable say ‘n’ which holds the value of number of terms in series.
  • Prompt the user to enter a number as value of n.
  • Call a user defined method m1() and pass ‘n‘ as parameter.
  • Inside method declare an integer variable say ‘sum‘ and initialize it to 0.
  • Use a for loop from i=1 to i<=n
  • Inside for loop we will multiply i*(i+1) and add with sum.
  • Print the result.

Program:

import java.util.*;
public class Main
{
    public static void main(String[] args)
   {
        // creating object of scanner class 
        Scanner s = new Scanner(System.in);
        //Taking input of number of elements in the series
        System.out.println("Enter the value of last exponent 'n' ");
        int n = s.nextInt();
       // calling m1 method to print the series
        m1(n);
   }
    public static void m1(int n)
    {
        //for loop to print the series
        int sum = 0;
        for (int i = 1; i <= n; i++)
            sum += i * (i + 1);
        System.out.println("Sum of the series is  " + sum);
    }
}

Output:

Enter the value of last exponent 'n' 
10
Sum of the series is 440

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