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
Factors Leaving a Specific Remainder
1577
26
Counting N Where N^N Is a Perfect Cube
1515
16
Greatest Product from an Integer Equation
1292
18
Counting Integer Pairs Satisfying an Equation
1353
13
Modular Liftoff
1698
21
A Modest Modular Power
1500
10
Binary Strings with Exactly Three 1's
1527
12
Chasing a Hundred Zeros
1500
12
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