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
Remainders on division
833
4
Smallest n for a Multiple Condition
833
4
Snoozing Alarms
833
2
Coin Combination Sum
750
3
Consecutive Integers with a Given Product
750
3
Large Power Remainder
833
3
Largest Perfect Square Not Expressible as a Floor Sum
1708
7
Minimizing the Largest Term of an Increasing Sequence
1167
3
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