Problem 2982. Get a Fibonacci number's index.

Created by Jared Metzel

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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 .

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40 Solutions
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Last Solution submitted on Dec 19, 2019

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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.

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