Comments on: Project Euler: Problem 25

By: Mokhtar

Mokhtar — Mon, 20 Jun 2011 17:04:43 +0000

amazing formula, I love solving project euler problems using mathematical tricks.
it makes me keep learning and loving math.
thank you.

By: Torleif

Torleif — Mon, 14 Mar 2011 17:39:39 +0000

Oh, maybe that’s the issue. Think it should be base 10!

By: Jo Hannes

Jo Hannes — Sun, 13 Mar 2011 17:17:44 +0000

Could it be, that you used a logarithm to another base? I get the result 2077, when i use logarithm with base e.

By: Torleif

Torleif — Tue, 18 Jan 2011 09:44:26 +0000

Really not sure why this is not working… Checked my C# code now, and it gives the right answer…

return (int) Math.Ceiling((1000 + Math.Log10(5) / 2 - 1) / Math.Log10(Constants.GoldenRatio))

GoldenRatio is the double 1.61803.

By: Torleif

Torleif — Thu, 06 Jan 2011 15:21:27 +0000

Hm, that’s strange. When I did this in C# I am pretty sure I got the right answer. Both from my bruteforce and the mathematical way of doing it. When I try to use the same programming formula in PHP here now, I get a different answer… can’t try out the C# version now, but will see if I can check it out later some time.

Must perhaps be an error in my formula? Or maybe PHP and your TI-89 works with a different precision than C#, or something like that? Let me know if you figure it out.

What answer did you get? With PHP I got 2077, which of course is wrong…

By: luiscencio

luiscencio — Wed, 05 Jan 2011 20:25:11 +0000

hi…. i used your formula… it gives me a wrong answer =) no offense
I am using a ti-89

I get a 4 digit not a 1000 digit. I mean… I enter what i got from the formula and it tells me its an incorrect answer =( sad

wish i could send you a screenshot =(

By: 10 one-line solutions for project euler | united-coders.com

10 one-line solutions for project euler | united-coders.com — Wed, 29 Dec 2010 11:46:38 +0000

[...] to (n)*Phi=(n+1), where Phi is the Golden Ratio: (1+sqrt(5))/2 – detailed description can found on geekality.net. def [...]