# 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:

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”.