**C Code:**

**#include**<stdio.h>

**#include**<math.h>

**int**

**main**(){

**int**a,d,n,i,tn;

**int**sum=0;

printf("Enter
the first number of the A.P. series: ");

scanf("%d",&a);

printf("Enter
the total numbers in the A.P. series: ");

scanf("%d",&n);

printf("Enter
the common difference of A.P. series: ");

scanf("%d",&d);

sum
= ( n * ( 2 * a + ( n -1 ) * d ) )/ 2;

tn = a + (n-1) * d;

printf("Sum of
the series A.P.: ");

**for**(i=a;i<=tn; i= i + d ){

**if**(i != tn)

printf("%d +
",i);

**else**

printf("%d = %d
",i,sum);

}

**return**0;

}

**Sample output:**

Enter the first number of
the A.P. series: 1

Enter the total numbers in
the A.P. series: 5

Enter the common difference
of A.P. series: 3

Sum of the series: 1 + 4 + 7
+ 10 + 13 = 35

**Definition of arithmetic progression (A.P.):**

A series of numbers in which
difference of any two consecutive numbers is always a same number that is
constant. This constant is called as common difference.

**Example of A.P. series:**

5 10 15 20 25 …

Here common difference is 5
since difference of any two consecutive numbers for example 20 – 15 or 25 -20
is 5.

**Sum of A.P. series:**

S

_{n}= n/2(2a + (n-1) d)**T**

_{n}term of A.P. series:
T

_{n}= a + (n-1) d
6. Write a c program to find out the sum of given H.P.