I'm building a resources page for a website that I built called numberthon (https://numberthon.com/) and I was wondering:

What are the most genius math tricks that you know?

Not necessarily useful tricks, but ones that make you fall in love with math (or at least think: "wait… that’s actually incredible").

For example, one of my favorites is the divisibility-by-3 trick:
if the sum of the digits is divisible by 3, then the original number is divisible by 3.

It’s so simple, but the fact that it always works feels almost magical.

What are your favorite tricks?

USAMO Guide is a free, open-source platform for math competition preparation covering everything from AMC 8 through USAMO and USAJMO. It is built and maintained entirely by high school students, with no institutional backing and no paywall. The platform has reached over 100,000 users, with thousands of students visiting every day from across the United States and around the world.

We're looking for a few more builders to join the team. Specifically, we're looking for people who can write and develop the lessons that students actually use to prepare for competitions.

This is an active contributor role. We want people with a strong Olympiad math background, generally AIME qualification or above, who are comfortable writing complete proofs instead of only solving problems. If you enjoy explaining why a solution works just as much as finding it, you'll probably enjoy this.

What you'll do

• Write MDX lessons on olympiad topics. Think of it as creating a cleaner, more intuitive alternative to the AoPS Wiki for students training for USA(J)MO.
• Create examples, practice problems, and diagrams that help difficult ideas make sense.
• Work within an established writing style and course structure alongside other contributors.

Trial period

Because students rely on our content to prepare for real competitions, every new builder starts with a one-month trial.

During this period, you'll contribute lessons, receive feedback, and work with the team while we evaluate whether it's a good fit. If everything goes well, you'll become a full builder, and the trial month will count as your first month on the team. If it doesn't work out, that's completely fine. We'd rather be upfront about expectations than have a long list of inactive contributors.

Our goal is to keep a team of people who consistently build and improve the platform.

What you get out of it

• Direct impact on a platform tens of thousands of students actually use to prep for real competitions
• A byline / credited authorship on your content
• A genuinely strong thing to point to for college apps: "co-author, [topic], USAMO Guide" is a specific, verifiable contribution, unlike some vague club title
• A team of people who are extremely into math just like yourself!!

How to apply:

Read the Info Packet :))

https://docs.google.com/document/d/1AUNOq6OlVcSZN_gUPfvyhimlh9hA4GNvNaLdzyflX_8/edit?usp=sharing

If you're unsure whether you're qualified, apply anyway. We'd much rather review your application than have you rule yourself out.

If there is any information that you want/doubts you have, please just comment them, and I will respond asap!