This equation computes the sum of n terms of a sequence of real numbers, which in this case is an arithmetic series. An arithmetic series is defined to be a set of numbers separated by a constant., d.. To find the sum, `S_n`, of the first n terms of an arithmetic series, uses the formula, Sn = n/2(2a1 + (n-1)d).
Input Variables:
Output for Formula:
Returns the sum of the terms of the arithmetic series