Category
Number Theory
Primes, divisibility, and modular arithmetic worth the detour.
Number theory is the study of the integers, and it is where elementary tools go furthest. Divisibility, primes and modular arithmetic settle questions that look far out of reach.
Problems here range from digit puzzles and divisibility arguments up to congruences, Diophantine equations, and orders modulo n. Checking small cases is not cheating — it is usually how the pattern gets found.
Latest problems
137 problems
Bounded Sum of Squares
1000
7
Divisible by One, Not Another
917
6
Divisor Probability
917
6
Exponents from a Factorization
917
3
Modular Congruence
917
2
Reciprocal Equation Solutions II
1000
2
Sum of Extreme Three-Digit Palindromes
917
1
A Repeating Decimal as a Fraction
833
8
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