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

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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:

 // C++ program for Nth odd fibonaci number    #include 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; }

 // 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

 # 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

 // 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

Output:
5

Time Complexity: O(N)

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