The Fibonacci Series/ Sequence in Python – The Easiest Way

Garvit Parakh | November 1, 2021 | Python examples | No Comments

In this Python example, we will discuss the different ways by which we can get the sequence of the Fibonacci Series. Let’s begin.

Table of Contents

1. What is Fibonacci Series/ Sequence?

The Fibonacci sequence is one of the simplest and earliest known sequences defined by a recurrence relation, and specifically by a linear difference equation.
– According to Wikipedia

In mathematics, the Fibonacci Series is a series of numbers that is formed using the sum of the two preceding numbers.

Example:

Input :  7   #Value of the index till which the user want series
Output : 1, 1, 2, 3, 5, 8, 13

Input : 12
Output : 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144

Some of the topics which will be helpful for understanding the program implementation better are:

Let’s implement different ways and understand each of them one by one.

2. Python Programs to Print The Fibonacci Series

There are different ways by which we can find the factorial of a number. We will go through each of the methods and see how they can be implemented.

2.1. How to Print The Fibonacci Series Using The Iteration Method

In the program, we have defined a function(fib_series) that has certain conditions using the if…else… and the while loop to print the series.

# Python program to get the Fibonacci series
def fib_series(n):

  n1, n2 = 0, 1
  count = 0

  if n < 0:
    print("Incorrect input, please try again!")

  elif n == 0:
    return 0

  elif n == 1 or n == 2:
    return 1

  else:
    print("Fibonacci sequence till the provided nth-term:")
    while count < n:
      print(n1, end=" ")
      nth = n1 + n2
      n1 = n2
      n2 = nth
      count += 1
      if count == n:
        break


# Main
n = int(input("Enter the nth-term to display the Fibonacci Series : "))
fib_series(n)

Output
Enter the nth-term to display the Fibonacci Series : 12
Fibonacci sequence till the provided nth-term:
0 1 1 2 3 5 8 13 21 34 55 89

2.2. How to print N-th Term of Fibonacci using Iterative Method

In this method, we will print the nth term of the Fibonacci series rather than the whole series.

# Python Program to find nth fibonacci term in space efficient manner
def fib(n):
  a1 = 0
  a2 = 1

  if n < 0:
    print("Input Incorrect, try again.")

  elif n == 0:
    return 0

  elif n == 1:
    return a2

  else:
    for i in range(1, n):
      a3 = a1 + a2
      a1 = a2
      a2 = a3
    return a2


# Main
n = int(input("Enter the nth term: "))
print("The nth term is:", fib(n))

Output
Enter the nth term: 22
The nth term is: 17711

2.3. How to print N-th Term of Fibonacci using Recursion method

In this program, we will implement the code to get the nth term using the recursion method

# Python Program to find nth fibonacci term using reursion
def fib(n):

  if n < 0:
    print("Incorrect input")

  elif n == 0:
    return 0

  elif n == 1 or n == 2:
    return 1

  else:
    return fib(n-1) + fib(n-2)


# Driver Program
n = int(input("Enter the nth term: "))
print("The nth term is:", fib(n))

3. Conclusion

In this example, we have discussed the different ways by which we can find the Fibonacci series and the nth term using the recursion and iterative methods.

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Complete code samples are present on Github project.

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