In programming, a program module or subroutine that calls itself to perform an iterative operation; in other words, a pure expression repeats itself to achieve a much more complex operation.
The Principle of Recursion is illustrated by Fibonacci numbers, a number series in which the first two terms are 1; successive terms are given by summing the two previous terms (1,1, 2, 3, 5, 8,13, 21, 34, 55, 89, 144, etc.). Fibonacci numbers can be generated by the following equation, as long as n is greater than 2: Fibonacci («) = Fibonacci (« – 1) + Fibonacci (n – 2).