RSS Feedsecure_iconYou are currently using a secure connection

Proposed Release Schedule for New Problems

All dates/times are showing for Europe/London timezone.

  • Problem 517: Saturday, 23rd May 2015, 01:00 pm
  • Problem 518: Saturday, 30th May 2015, 04:00 pm
  • Problem 519: Saturday, 6th June 2015, 07:00 pm

Recent News

10 April 2015: New Awards

A number of new awards have been added and there has been a minor change to one of the awards.

  • Centurion (solve 100 consecutive) has been removed and the following have been added: Flawless Fifty (solve 50 consecutive problems), C for Commitment (solve the first 100 problems), CC for Continued Commitment (solve the first 200 problems), and D for Dedication (solve the first 500 problems).
  • Two difficulty based awards have been added: Easy Prey (solve 25 of the 50 easiest problems) and Big Game Hunter (solve 25 of the 50 hardest problems).
  • Two awards relating to the archives have been added: The Archivist (solve half the problems in the archives) and Master of Archives (solve every problem in archives).

We hope that you enjoy these new awards and they add to the fun as you continue solving the problems.

19 February 2015: Difficulty Ratings

After considerable work behind the scenes the team is pleased to announce the introduction of a difficulty rating system.

Difficulty ratings are based on the times taken to solve a problem since its publication date. For problems 277+ the data is taken from the fastest solvers tables and for older problems we are making use of data points taken from historical snapshots.

Due to the instability of the difficulty index with limited data it is not possible to provide a meaningful metric for newly released problems. Consequently we have separated the ten most recent problems (found under the new menu bar "Recent") from the rest of the problems (now called "Archives" in the menu). Recent problems will not have a difficulty rating and any problems in the Archives for which the fastest solvers table is not full will indicate that the rating is "not yet finalised".

Each problem in the Archives is given a difficulty rating ranging from 5% to 100% (in 5% increments). Within each of those twenty bands problems are then sorted by ID. Of course, no difficulty system is going to be perfect, and there are likely to be anomalies, but we hope that you find the system we have introduced provides a generally useful guide.

24 January 2015: Problem 500

Saturday 31st of January Project Euler will reach a major milestone with the publication of our 500th problem.
To celebrate this the team has composed a special problem in which the number 500 occurs repeatedly.
In addition we're going to publish an ordinary problem simultaneously as problem 501. Both problems are published at 13:00 London time.

We invite all members to participate in our problem solving party. As celebrator of this jubilee we're allowed to ask the participants for a present.
Well, here's our wish: please don't share any information about our party and the dishes we're serving you outside the fora dedicated to our dishes after your meal.
This to allow those that are late to the party to consume our dishes undisturbed by premature revelations about what we are serving.

15 September 2014: Emergency Account Recovery Key

Since we no longer store any personal information in the database it has not been possible to gain access to your account if you forget your password. It is also possible that some members have changed their username and after a period of absence from Project Euler they have forgotten what they changed it to.

To help members protect against accidentally losing access to their own accounts we have introduced an emergency account recovery key. If you have not done so already then the Account tab in the menu bar should be highlighted to indicate that something needs to be done. When you visit your account page you will be prompted to generate your key. After clicking the button you will be presented with your own personal randomly generated key and advised that after making a careful note of it to store it in a safe location.

In order to protect your account only a hash of your key is stored in the database. This means that the server will be unable to display your key again once you navigate away from that page.

In the event of losing your password and/or username then you will find an additional link on the Sign In page to recover your account. On that page you will need to enter the entire key, and correctly enter a CAPTCHA code. If the key is authenticated then on the next page you will be reminded of your username and a new password will be generated.

Your key will continue to work as often as you need it, but if you suspect that it has been compromised then you can generate a new key on your account page. But please be aware that generating a new key will make the old key invalid.

You are personally responsible for safe-guarding your own key and it is the only alternative mechanism available to gain access to your account in the event of losing your primary sign-in credentials.

8 September 2014: Remember Me, HTTPS, and Privacy Policy

Many members will be pleased to see that the "Remember Me" feature has been restored. When you sign in now you can tick the box to keep your session alive. You can sign out in the normal way, otherwise your session will remain active for up to 30 days of inactivity.

You may also have noticed that the default connection to the website is now secure (HTTPS). It is still possible to switch between non-secure and secure using the padlock icon in the top right corner of each page.

In order for these features to be enabled it has been necessary to use cookies. At the bottom of each page, next to the link for copyright information, a new link has been added to outline our privacy policy. This explains in details which cookies are used, what data is stored in the database, and what information is public by default.