# Python Program Fibonacci Series Function

By | April 24, 2020

Topic: Python Program Fibonacci Series Function

Write a user defined Fibonacci functin in Python to print the popular Fibonacci series up to the given number n. Here n is passed as an argument to the Fibonacci function and the program will display the Fibonacci series upto the provided number by the user input. Python Fibonacci Series Function Program

## What is a Fibonacci Series?

### Definition of Fibonacci Series

The Fibonacci Sequence is the series of numbers, such that every next number in the fibonacci series is obtained by adding the two numbers before it:

Fibonacci series is – 0,1,1,2,3,5,8,13,21,34,55,89,144,233,377

Note: First two numbers in the Fibonacci series are 0 and 1 by default.

Examples:

Therefore third number or term 2 in the Fibonacci series is obtained by adding the two numbers before it that is, 0 and 1.
Similarly the fourth term 3 is obtained by adding the two numbers 1 and 2, before it, and so on.

## Who invented the Fibonacci Series?

The popular Fibonacci series was invented by an Italian mathematician Leonardo of Pisa (aka Fibonacci) (1175 AD to 1250 AD.)

## Why Leonardo Invented Fibonacci Series?

The real story behind the invention of the Fibonacci series is that: This series is invented by Leonardo because he was to solve a real life problem about the Rabbits farming. A rabbit farmer wanted to know how many rabbits he can grew in a year from one pair. The problem is solved by Fibonacci series by knowing and considering the following facts about the rabbit’s life. “A pair of rabbits bear another new pair in a single month. This new born pairs can bear another pair after the first month”.

Python Source Code for Python Fibonacci Series Function Program

```# Write a Python 3 program to input a number n
# and show the Fibonacci series up to that
# number using a user defined function
# www.EasyCodeBook.com

# define the user defined function
# to print the Fibonacci series up to n
def fibonacci(n):
"""This function Prints the Fibonacci series up to n."""
a, b = 0, 1
while a < n:
print(a, end=' ')
a, b = b, a+b
print()

def main():
n = int(input("Enter a number n to show Fibonacci series upto n:"))
fibonacci(n)

main()

```

Output

```Enter a number n to show Fibonacci series upto n:100
0 1 1 2 3 5 8 13 21 34 55 89

Enter a number n to show Fibonacci series upto n:1000
0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987
```

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