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
Day of the Week - Christmas
833
5
Distinct Prime Digit Count
833
3
Four-Digit Multiples Count
833
5
GCD-LCM Sum Minimization
917
5
Least Perfect Square Multiple
833
4
Modular Exponentiation
833
2
Ones in Binary from 1 to 128
1542
5
Prime Factors of a Factorial Ratio
833
4
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