Number Theory

Primes, divisors, GCD, modular arithmetic and bases.

51 problems

Title	Tags	Acceptance	Difficulty
1. Product Modulo	Modular Arithmetic	—	Easy
2. Factorial	Math · Big Integer	—	Easy
3. N-th Fibonacci Modulo	Fast Doubling · Matrix Power	—	Medium
4. Primes up to N	Sieve	—	Easy
5. Prime Factorisation	Factorisation	—	Easy
6. Number of Divisors	Divisors	—	Easy
7. Sum of Divisors	Divisors	—	Easy
8. Perfect Number	Divisors	—	Easy
9. Armstrong Number	Digits	—	Easy
10. Reverse an Integer	Digits	—	Easy
11. Palindrome Number	Digits	—	Easy
12. Digital Root	Digits · Modular Arithmetic	—	Easy
13. LCM of an Array	GCD · LCM	—	Easy
14. Modular Exponentiation	Fast Power	—	Medium
15. Modular Inverse	Extended Euclid · Fermat	—	Medium
16. Combinations nCr	Combinatorics	—	Easy
17. Catalan Number	Combinatorics	—	Medium
18. Digits of N!	Logarithms	—	Medium
19. Collatz Steps	Simulation	—	Easy
20. Decimal to Any Base	Number Bases	—	Easy
21. Any Base to Decimal	Number Bases	—	Easy
22. GCD of an Array	GCD	—	Easy
23. Euler's Totient	Totient	—	Medium
24. Sum of Two Squares	Two Pointers · Math	—	Medium
25. Goldbach Pair	Primes	—	Medium
26. Primes in a Range	Sieve · Prefix Sum	—	Medium
27. Pythagorean Triplets	Brute Force	—	Medium
28. Power of Two	Bits	—	Easy
29. Happy Number	Cycle Detection	—	Easy
30. N-th Ugly Number	Dynamic Programming	—	Medium
31. Excel Column Title	Number Bases	—	Easy
32. Excel Column Number	Number Bases	—	Easy
33. Integer Square Root	Binary Search	—	Easy
34. Integer K-th Root	Binary Search	—	Medium
35. Sum of All Digits 1..N	Digit DP	—	Hard
36. Sum of Squares 1..N	Formula	—	Easy
37. Leap Years in a Range	Inclusion–Exclusion	—	Easy
38. Clock Angle	Geometry	—	Easy
39. Triangle Type	Geometry	—	Easy
40. Polygon Area	Geometry · Shoelace	—	Medium
41. Points in Rectangle	Geometry	—	Easy
42. Perfect Squares	Dynamic Programming	—	Medium
43. Steps to Reduce a Number to Zero	Simulation · Bit Manipulation	—	Easy
44. Bulb Switcher	Math	—	Medium
45. Integer Replacement	Greedy · Bit Manipulation	—	Medium
46. Valid Perfect Square	Binary Search	—	Easy
47. Arranging Coins	Math · Binary Search	—	Easy
48. Power of Three	Math	—	Easy
49. Self-Dividing Numbers	Math	—	Easy
50. Count Odd Numbers in a Range	Math	—	Easy
51. Product Minus Sum of Digits	Math	—	Easy

51 of 51 problems