Go Pro!

Divisibility Rules

Reference > Mathematics > Number Theory
How to tell if a number is divisible by a power of two.
Divisibility rules for three, six, and nine
Divisibility rules for five, ten, twenty-five, and one hundred
Lesser known, and much less practical divisibility rules for seven and eleven
Divisibility rule for eleven - alternating digits

Understanding Coronavirus Spread

A Question and Answer session with Professor Puzzler about the math behind infection spread.

Blogs on This Site

Reviews and book lists - books we love!
The site administrator fields questions from visitors.
Like us on Facebook to get updates about new resources
Pro Membership