# Number Theory

Pro Problems > Math > Number and Quantity > Number Theory# Featured Pro Problems

Without a calculator find a nine digit number that meets the criteria of the problem

A math problem involving Shrek wanting Fiona's telephone number

Strings of red lights and green lights on my Christmas tree - a Christmas word problem

A diophantine equation - quadratic in two variables

Use divisibility rules to determine the number with missing digits

Given two pieces of information about the three digit number, determine all possible values.

Solve an algebra problem involving a defined binary operation (the hashtag or pound symbol)

Find the sum of two binary numbers, write the answer in base ten

# Full Directory Listing

Crossing Out Numbers, How many zeroes?, Nine Digit Number, Pyramid of Blocks# Understanding Coronavirus Spread

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

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Reviews and book lists - books we love!

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