A succession of numbers formed according to some definite rule is called a sequence alternatively a sequence is a kind of mapping, where domain always is a set of a natural numbers (finitely or infinitely) and range may be a real or complex numbers. In mathematical form

Sequences ≡ f : N_n → X

 

Where N_n denotes set of first n natural numbers (1, 2, 3, N). For finite n we call it finite sequence and for infinite n we call it infinite sequence. If X = R then we call the sequence f is a real sequence and if X = C, we call f is a complex sequence.

 

 

Not necessary, if the terms of a sequence follow certain pattern or rule then it is called progression. Here we are discussing following progression:

(i)    Arithmetic Progression (A.P.)

(ii)   Geometric Progression (G.P.)