sum of consecutive numbers in java

Sum of any number which are in sequence from start to end , there is a mathematical formula to calculate the sum of the given number if they are in sequence is
sum=n(Fisrt_Number+Last_Number)/2 , where n is the count of given numbers for example: sum of 20, 21, 22, 23, 24, 25 can be calculated as: sum=6(20+25)/2 =135 , here n is 6 which is total given number’s, below a java program is written to calculate the same using the given formula.

int totalSum = length * (firstNum + lastNum) / 2;
package com.il.basics.programs;

import java.util.Arrays;

public class SumOfNConsecutiveNumbers {

	public static void main(String[] args) {
		int array[] = { 20, 21, 22, 23, 24, 25 };
		int length = array.length;
		int firstNum = array[0];
		int lastNum = array[length - 1];
		int totalSum = length * (firstNum + lastNum) / 2;
		System.out.println("Sum of " + Arrays.toString(array) + " is: "
				+ totalSum);
	}
}
******output*******
Sum of [20, 21, 22, 23, 24, 25] is: 135

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