Welcome to my home page!
Welcome to my home page!
Welcome to my home page!
Using Lean or other programmable proof assistants to solve Project Euler is the inevitable collision of two autisms. In particular, using Lean to prove that you have the correct solution, just making a Lean program that prints out the correct solution is likely now trivial as of 2025 by asking an LLM to port a Python solution to the new language.
Some efforts:
- github.com/mfornet/project-euler-lean Attempts proofs, but only did Project Euler problem 1 :-)
- github.com/pcpthm/pe solved the first 50, but as stated on the README itself, no proofs, so boring
- unreasonableeffectiveness.com/learning-lean-4-as-a-programming-language-project-euler/ solves 4, but no proofs
Mentions:
- Alex J. Best (Jun 29 2022 at 14:20) on the Lean Zulip mentions:That dude was actually working at harmonic.fun as of 2025, bastard.
It would also be very interesting to collect verified fast Project Euler solutions for Lean 4 at some point, this would simultaneously work out the compiled speed and the mathematics libraries which would be fun.
- codeforces.com/blog/entry/124615
In other proof assistants, therefore with similar beauty:
- Coq
- github.com/airobo/Project-Euler-in-Coq: 1 and 2 with proofs
Repositories of numerical solutions:
Repositories of code solutions:
- euler.stephan-brumme.com/ large number of solutions in C++, stopped around 600. Informal permissive license, e.g. at: euler.stephan-brumme.com/243/Asked for a more formal open license at: github.com/stbrumme/euler/issues/7All of my solutions can be used for any purpose and I am in no way liable for any damages caused.
- www.ivl-projecteuler.com/home 330+ solutions in Python as of 2025. Random looking problem selection. On GitHub: github.com/igorvanloo/Project-Euler-Explained under Unlicense license, a public domain license.
- www.nayuki.io/page/project-euler-solutions. Large number of solutions, mostly in Java and Python primarily but also Mathematica and Haskell sometimes. Proprietary license.
Repositories with hints but no solutions:
Project Euler problems typically involve finding or proving and then using a lemma that makes computation of the solution feasible without brute force. There is often an obvious brute force approach, but the pick problem sizes large enough such that it is just not fast enough, but the non-brute-force is.
news.ycombinator.com/item?id=7057408 which is mega high on Google says:
I love project euler, but I've come to the realization that its purpose is to beat programmers soundly about the head and neck with a big math stick. At work last week, we were working on project euler at lunch, and had the one CS PhD in our midst not jumped up and explained the chinese remainder theorem to us, we wouldn't have had a chance.
In many cases, the efficient solution involves dynamic programming.
There are also a set of problems which are very numerical analysis in nature and require the approximation of some real number to a given precision. These are often very fiddly as I doubt most people can prove that their chosen hyperparameters guarantee the required precision.
Many problems ask for solution modulo some number. In general, this is only so that C/C++ users won't have to resort to using an arbitrary-precision arithmetic library and be able to fit everything into
uint64 instead. Maybe it also helps the judge system slightly having smaller strings to compare. The final modulos usually don't add any insight to the problems.Bibliography:
Saw this one mentioned on some Project Euler forum threads.
Nice motto, knowledge olympiads:
Serious mathematics for serious high-school students: There is more to mathematics than competitions.
TODO none? Seriously?
Pinned article: Introduction to the OurBigBook Project
Welcome to the OurBigBook Project! Our goal is to create the perfect publishing platform for STEM subjects, and get university-level students to write the best free STEM tutorials ever.
Everyone is welcome to create an account and play with the site: ourbigbook.com/go/register. We belive that students themselves can write amazing tutorials, but teachers are welcome too. You can write about anything you want, it doesn't have to be STEM or even educational. Silly test content is very welcome and you won't be penalized in any way. Just keep it legal!
Intro to OurBigBook
. Source. We have two killer features:
- topics: topics group articles by different users with the same title, e.g. here is the topic for the "Fundamental Theorem of Calculus" ourbigbook.com/go/topic/fundamental-theorem-of-calculusArticles of different users are sorted by upvote within each article page. This feature is a bit like:
- a Wikipedia where each user can have their own version of each article
- a Q&A website like Stack Overflow, where multiple people can give their views on a given topic, and the best ones are sorted by upvote. Except you don't need to wait for someone to ask first, and any topic goes, no matter how narrow or broad
This feature makes it possible for readers to find better explanations of any topic created by other writers. And it allows writers to create an explanation in a place that readers might actually find it.
Figure 1. Screenshot of the "Derivative" topic page. View it live at: ourbigbook.com/go/topic/derivativeVideo 2. OurBigBook Web topics demo. Source. - local editing: you can store all your personal knowledge base content locally in a plaintext markup format that can be edited locally and published either:This way you can be sure that even if OurBigBook.com were to go down one day (which we have no plans to do as it is quite cheap to host!), your content will still be perfectly readable as a static site.
- to OurBigBook.com to get awesome multi-user features like topics and likes
- as HTML files to a static website, which you can host yourself for free on many external providers like GitHub Pages, and remain in full control
Figure 3. Visual Studio Code extension installation.
Figure 4. Visual Studio Code extension tree navigation.
Figure 5. Web editor. You can also edit articles on the Web editor without installing anything locally.Video 3. Edit locally and publish demo. Source. This shows editing OurBigBook Markup and publishing it using the Visual Studio Code extension.Video 4. OurBigBook Visual Studio Code extension editing and navigation demo. Source. 
- Infinitely deep tables of contents:
All our software is open source and hosted at: github.com/ourbigbook/ourbigbook
Further documentation can be found at: docs.ourbigbook.com
Feel free to reach our to us for any help or suggestions: docs.ourbigbook.com/#contact