nth Fibonacci number in python

Hi, today we will learn how to find nth Fibonacci number in python.  At first, we should know about what is the Fibonacci series.

Find nth Fibonacci number in Python

Fibonacci Series:

Basically Fibonacci series is a series which follows a special sequence to store numbers.



Rule: ( 2nd previous number + 1st previous number ) = 3rd number ( Current number ).

Series: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34…….

Explanation:

  1. 0 is the first number
    Then series = 0
  2. 1 is the 2nd number
    Then series = 0,1  ( after 1 the Fibonacci rule started )
  3. (0+1) = 1
    Then series = 0,1,1
  4. (1+1) = 2
    Then series = 0,1,1,2
  5. (1+2) = 3
    Then series = 0,1,1,2,3
  6. (2+3) = 5
    Then series = 0,1,1,2,3,5
  7. (3+5) = 8
    Then series = 0,1,1,2,3,5,8
  8. (5+8) = 13
    Then series = 0,1,1,2,3,5,8,13
  9. (8+13) = 21
    Then series = 0,1,1,2,3,5,8,13,21
  10. (13+21) = 34
    Then series = 0,1,1,2,3,5,8,13,21,34 and so on..

Here is the optimized and best way to print Fibonacci sequence: Fibonacci series in python (Time complexity:O(1))

Get the nth number in Fibonacci series in python

This article covered how to create a Fibonacci series in python. This python program is very easy to understand how to create a Fibonacci series. After the creation of a Fibonacci series, we can find the nth Fibonacci number in the series.

Code:

n = int(input('Enter : '))
fibo_nums = [0,1]
i=1
if(n==1 or n==2):
    print(n,'th Prime Number is :',fibo_nums[n-1])
    print('Fibonacci Series :', fibo_nums)
elif(n>2):
    while (True):
        fib = fibo_nums[i-1]+fibo_nums[i]
        fibo_nums.append(fib)
        if(len(fibo_nums)==n):
            break
        else:
            i+=1
    print(n,'th Fibonacci Number is :', fibo_nums[n-1])
    print('Fibonacci Series is :', fibo_nums)
else:
    print('Please Enter A Valid Number')

Output:

Enter : 5
10 th Fibonacci Number is : 3
[0, 1, 1, 2, 3]

Code Explanation:

  • At first, we take the nth value in the ‘n’ variable.
  • We create a ‘fibo_nums’ list variable and initially we store 0,1.
  • We create an int variable ‘i’ and initially we store 1.
  • We check if the value of n is 1 or 2. if the condition satisfied then we can direct print the required nth Fibonacci number from the ‘fibo_nums’ list variable without performing any series creation operation.
  • We check if the value of n is greater than 2. if the condition satisfied then we start an infinite while loop, and the breaking condition is if the length of the ‘fibo_nums’ list is equal to the ‘n’ variable. Inside the while loop, Fibonacci series creation operation is performed. we create a ‘fibo’ variable, and we store the value of 2nd previous number + 1st previous number according to the current ‘i’ value. Then we append/add the value of ‘fibo’ into the ‘fibo_nums’ list.
  • Then we print the ‘n – 1’ position value of ‘fibo_nums’ list as a result ( nth Fibonacci number). And we also print the ‘fibo_nums’ list as the Fibonacci series.
  • In else part we print “Please enter a valid number”.

 

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