The Recursion is a powerful method for simplify the design of the algorithms. Principally, the recursion means the self-reference. In the recursive mathematical series, each word is derived by applying the formula to the preceding terms. The Fibonacci series (1, 1, 2, 3, 5, 8, 13, 21, ...), that was first used to model the growth of the rabbit colony, is an example. Each word in the series (after the second) is the sum of the two terms that instantly precede it.
In a recursive description, somewhat is defined in terms of the simpler versions of itself.
Consider the definition of n factorial (n!), that the product of all integers from 1 to n:
n! = n * (n - 1)!