Program to find Nth odd Fibonacci Number

Given an integer N. The task is to find the Nth odd Fibonacci number.

The odd number fibonacci series is as:

1, 1, 3, 5, 13, 21, 55, 89, 233, 377, 987, 1597………….and so on.

Note: In the above series we have omited even terms from the general fibonacci sequence.

Examples:



Input: N = 3
Output: 3

Input: N = 4
Output: 5

Approach:
On observing carefully, it can be deduced that every third Fibonacci number is even, so the Nth odd Fibonacci number is the {(3*N+1)/2}th term in the general Fibonacci sequence.

Below is the implementation of the above approach:

filter_none

edit
close

play_arrow

link
brightness_4
code

// C++ program for Nth odd fibonaci number
  
#include <bits/stdc++.h>
using namespace std;
  
// Function to find nth odd fibonaci number
int oddFib(int n)
{
    n = (3 * n + 1) / 2;
    int a = -1, b = 1, c, i;
    for (i = 1; i <= n; i++) {
        c = a + b;
        a = b;
        b = c;
    }
    return c;
}
  
// Driver Code
int main()
{
    int n = 4;
      
    cout << oddFib(n);
      
    return 0;
}
chevron_right

filter_none

edit
close

play_arrow

link
brightness_4
code

// Java program for Nth odd fibonaci number 
class GFG 
{
      
    // Function to find nth odd fibonaci number 
    static int oddFib(int n) 
    
        n = (3 * n + 1) / 2
          
        int a = -1, b = 1, c = 0, i; 
          
        for (i = 1; i <= n; i++) 
        
            c = a + b; 
            a = b; 
            b = c; 
        
        return c; 
    
      
    // Driver Code 
    public static void main (String[] args) 
    
        int n = 4
          
        System.out.println(oddFib(n)); 
    
}
  
// This code is contributed by AnkitRai01
chevron_right

filter_none

edit
close

play_arrow

link
brightness_4
code

# Python3 program for Nth odd fibonaci number
  
# Function to find nth odd fibonaci number
def oddFib(n):
    n = (3 * n + 1) // 2
  
    a = -1
    b = 1
    c = 0
    for i in range(1, n + 1):
        c = a + b
        a = b
        b = c
  
    return c
  
# Driver Code
n = 4
  
print(oddFib(n))
  
# This code is contributed by mohit kumar
chevron_right

filter_none

edit
close

play_arrow

link
brightness_4
code

// C# program for Nth odd fibonaci number 
using System;
      
class GFG 
{
      
    // Function to find nth odd fibonaci number 
    static int oddFib(int n) 
    
        n = (3 * n + 1) / 2; 
          
        int a = -1, b = 1, c = 0, i; 
          
        for (i = 1; i <= n; i++) 
        
            c = a + b; 
            a = b; 
            b = c; 
        
        return c; 
    
      
    // Driver Code 
    public static void Main (String[] args) 
    
        int n = 4; 
          
        Console.WriteLine(oddFib(n)); 
    
}
  
// This code is contributed by 29AjayKumar
chevron_right

Output:
5

Time Complexity: O(N)

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.





Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.



Article Tags :