Project Euler Forum

Hi all,

I haven't looked at the Project Euler site in a few months, as I've been busy with other things. I returned about half an hour ago, and noticed that some of the problem descriptions have changed. I'm wondering why.

For example, Problem 2, last time I looked at the site, asked for the sum of even numbers of the Fibonacci sequence up to one million. Now, it's asking for the sum up to four million.

Problem 3 previously asked for the largest prime factor of 317584931803. Now it's asking for the largest prime factor of a composite number, and in the problem description is specifying 600851475143 as the number.

Problem 10 previously asked to sum the primes below one million. Now it's asking to sum the primes below two million.

I haven't looked any further than this, so don't know what else might have changed. Even so, I'm curious to know why the problem descriptions of these three have changed.

Thanks...

There are indeed some other problems for which something has changed.
One of the reasons was that some idiot thought it a good idea to publish an answers list to a great many problems somewhere on the internet.
That list has disappeared by now. Also from Googles cache.
To discourage such undertakings we changed some limits or numbers in a way that would not make an algoritmic change to the problem . When we did so a small note was added to these problems.
As this was a few weeks ago this note has been removed by now.
Let it be clear that all problems may be subject without prior notice to some change when we think that a good idea.
For a short time there may be a notice. We even thought about adding a new feature to Project Euler: rotatable answers to promote more general solutions than solutions based on a certain limit or number.
Someone relying on external resources should always check that the current description is the one he is relying on.
Moreover it's a good idea to write a general solution to a problem.