A finite series is one with a finite number of terms and, for example, when

using the summation notation, the finite series a3/a4/. . ./a20 would be written


The summation index n is a dummy index, in the sense that it may be

replaced by any other symbol without changing the meaning of the summa-

tion, and thus

X n1

an X r1

ar . . . X s1


The following are four examples of infinite series with numerical terms.