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Contest portal
Where is my access code? It is in the confirmation email we sent from hello@combinatoricsopen.org when you registered. It starts with CO26-. Search your inbox for "CO26-" and check Spam and Promotions too. Cannot find it? Email hello@combinatoricsopen.org from the address you registered with.
Signing in does not start your clock.
Before you start
Signed in as . Use a different email
Test login. This run is for checking the page and is not a contest entry.
- You get 20 problems and 90 minutes. The clock starts when you press Start. It cannot be paused, and it keeps running if you close this page.
- Every answer is a whole number from −100 to 500. Leave a box empty if you have no answer.
- Your answers save automatically. You can change them until you submit or your time runs out. When time runs out, your saved answers are submitted for you.
- Use one device and one tab for the whole contest. If the page closes, open it again and sign in. Your answers and your clock are kept.
- Allowed: pen and paper, a dictionary, and a translation-only tool. Not allowed: AI tools or chatbots, calculators, other websites or software, and help from other people.
- Keep your written work. Do all your work on paper and write the problem number next to it. When you finish, photograph every page and keep the photos until final results on Nov 24. Contestants in range for an award will be asked for their work.
- To keep the contest fair, this page records when each answer is entered and when you leave this page.
- Do not share or discuss the problems until the window closes on Sunday Nov 15 at 23:59 UTC.
Test login. This run is not a contest entry.
Jump to a problem. Filled squares have an answer.
Finished early? Submit your final answers. After you submit, you cannot change them. If you do nothing, your saved answers are submitted when your time runs out.
Your answers are in
Backup code. If this page still says your answers were not confirmed after a few minutes, copy this code and email it to hello@combinatoricsopen.org from the address you registered with.
Your answers
What to do now
- Photograph every page of your written work now. Keep the photos and the paper until final results on Nov 24.
- Do not share or discuss the problems until the window closes on Sunday Nov 15 at 23:59 UTC.
- If your score is in range for an award, we will email you between Nov 16 and Nov 18 to ask for your work. Check your spam folder too.
- Problems and solutions are published on Nov 17. Preliminary results come on Nov 19 and final results on Nov 24.
Questions: hello@combinatoricsopen.org