2. Write a C++ program to calculate the sum of the integers between two numbers. The formula to calculate this sum is: sum=(2n)(2a+(n1)d) n is the number of integers to be added. a is the first number. d is the difference between each number. Note that the program must prompt the user to enter the values of a and n. For example, if the user wants to calculate the sum between 1 and 100,s/ he would enter 1 for a and 100 for n; and if the user wants to calculate the sum between 20 and 50 , s/he would enter 20 for and 30 for n