Number Theory
The secret lives of whole numbers.
- 17Primes and DivisibilityreadySpot primes, test divisibility in your head, break numbers into primes, and count the zeros at the end of a factorial.
0% - 18FactorsreadyEvery factor is a dot on a little grid of exponents: count the dots, add them up, or multiply them in pairs.
0% - 19GCD and LCMreadyFind the biggest shared divisor and the smallest shared multiple by sorting prime factors, and speed up the GCD with Euclid's square-cutting trick.
0% - 20Modular ArithmeticreadyWork with remainders instead of giant numbers: wrap around a clock dial, find last digits of huge powers, and combine remainder conditions.
0% - 21Diophantine EquationsreadyEquations where every answer must be a whole number: factor them, list the factor pairs, and let the integers do the work.
0% - 22Misc Number TheoryreadyPalindromes, coin puzzles, number machines and the Chicken McNugget theorem: a toolbox of number tricks for contest day.
0%