® By a sequence , we mean an arrangement of number in definite order according to some rule. Also, we define a sequence as a function whose domain is the set of natural numbers or some subsets of the type { , , , .... k }. A sequence containing a finite number of terms is called a finite sequence .
A sequence is called infinite if it is not a finite sequence. ® Let a , a , a , ... be the sequence, then the sum expressed as a + a + a + ... is called series .
A series is called finite series if it has got finite number of terms.