Problem 44311. Number of Even Elements in Fibonacci Sequence

Created by Mehmet OZC

Solve Later

Find how many even Fibonacci numbers are available in the first d numbers.

Consider the following first 14 numbers

1 1 2 3 5 8 13 21 34 55 89 144 233 377 ...

4 of them are even.

Solve

Solution Stats

1998 Solutions
433 Solvers

Last Solution submitted on Jan 22, 2020

Last 200 Solutions

Problem Comments

2 Comments

2 Comments

Ren Liujie on 22 Dec 2017

Big number is a problem. Instead we can find the regular pattern in which those even and odd numbers appear. Then everything becomes simple and easy.

Lamour Haithem Firass on 21 Sep 2019

i have the program on my matlab it work normaly but cody does not accepet the code don't know why?????
function y = evenFibo(n)
y(1) = 1;y(2) = 1;
for i = 3:n
y(i) = y(i-1) + y(i-2);
end
e = y;
E = mod(e,2) == 0;
evennumbers = e(E);
y = length(evennumbers);
if n > 2
fprintf('The even Fibo number is: %d',y)
end
end

Solution Comments

Solution 1865516

3 Comments

3 Comments

SJ Won on 4 Jul 2019

What's wrong with this?? It's working in matlab for me .

Lamour Haithem Firass on 21 Sep 2019

me2

goc3 on 23 Oct 2019

The fibonacci() function is in a toolbox. Only functions in vanilla Matlab are recognized by Cody.

Solution 1319950

3 Comments

3 Comments

Leo Nunnink on 30 Oct 2017

My code works to d=50 and fails on the higher values in the test suite. I think it is a hardware-limited rounding error (?swamping) with very large numbers. When I test eps(fibonacci(100)) on my system, the answer is 6.5 ie my system can not accurately distinguish odd from even at that large a number.

James on 2 Nov 2017

Leo, your theory is correct: The numbers that you're calculating for d>50 are too large to be represented by a 32-bit digit, and won't be calculated correctly for mod(x,2). Think very carefully about the number pattern in the Fibonacci sequence, and see if a pattern emerges.

Mehdi BENSEDDIK on 4 Apr 2019

Indeed, My code works until the d = 50 because it's a large number, so our algorithm is correct we should not worry about it, I think we have succeed in this challenge.

Solution 1318351

1 Comment

1 Comment

David Verrelli on 3 Nov 2017

Not a true solution. Would fail if Test Suite were expanded.

Solution 1302521

1 Comment

1 Comment

David Verrelli on 3 Nov 2017

Not a general solution. Will fail if Test Suite expanded.

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Problem 44311. Number of Even Elements in Fibonacci Sequence

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Problem 44311. Number of Even Elements in Fibonacci Sequence

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