Problem 2982. Get a Fibonacci number's index.

Created by Jared Metzel

Difficulty:Rate

Solve Later
Add To GroupÃ‚

N.B. For the purpose of this exercise, the first Fibonacci number is 1, and the second is 2; that is, fib(1) = 1 and fib(2) = 2 .

Make a function isfib(x) so that:

if the value of the input x is not a Fibonacci number, the function returns a zero.
if the value of the input x is a Fibonacci number, the function returns its index in the Fibonacci sequence. That is, isfib(fib(n)) should return the value of n .

Solve

Solution Stats

149 Solutions
46 Solvers

Last Solution submitted on Apr 21, 2025

Last 200 Solutions

Problem Comments

2 Comments

2 Comments

Jan Orwat on 13 Mar 2015

5.731478440138172e+20 from 7th test is not a Fibonacci Number. 100th Fibonacci Number in proposed convention is 573147844013817084101 which has 21 digits and exceeds double precision.

Rafael S.T. Vieira on 23 Sep 2020

I agree with Jan. http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Fibonacci/fibtable.html (this list begins at 0). The 100th fibonnaci number is 573147844013817084101 (5.731478440138171e+20), and not 5.731478440138172e+20.

Solution Comments

Show comments

FEATURED DISCUSSION

LLMs with MATLAB updated to support the latest OpenAI Models

Large Languge model with MATLAB, a free add-on that lets you access...

Toshiaki Takeuchi in Generative AI

View Post

Problem Recent Solvers46

Problem Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!