Summationsnotation
Summation notation, represented by the Greek letter Sigma (Σ), denotes the sum of a sequence of terms indexed by an integer variable. The general form is Σ_{i=a}^{b} f(i), where a and b are integers and f(i) is the term being summed. The sum runs over all integer values of i from a to b inclusive. If b is infinity, the notation describes an infinite series: Σ_{i=a}^{∞} f(i).
In finite sums, simple algebraic rules apply. Constants can be pulled out: Σ c·f(i) = c·Σ f(i). Sums
Infinite sums, or series, consider the sequence of partial sums S_n = Σ_{i=a}^{n} f(i). The series converges
Common results include geometric series: Σ_{k=0}^{∞} ar^k = a/(1−r) for |r| < 1, and the finite sum Σ_{k=0}^{n}