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
Not a Power
1167
2
Reciprocal Equation Solutions
1083
2
Smallest n for a Multiple Condition II
1333
3
Smallest Number with Given Divisor Count
1083
4
Trailing Zeros II
1083
3
Addition in an Unknown Base
1000
4
Counting Divisors II
1000
3
Counting Multiples
1000
3
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