Subcategories

• Day 5

  Base Conversion Factorial Mod 314 The Biggest Factor A String of 2's
  1
  Topics
  1
  Posts

  S

  10^n mod 7 is congruent to iii.) 3^n mod 7 but also congruent to v.) 17^n mod 7. They both should be correct but only iii.) is. Must be fixed

• Day 6

  Factorize 9991 Finding the Sum of Digits A Proof About Primes Base 10 to Base 9
  1
  Topics
  1
  Posts

  E

  In the video, the text question says 77 is in base 9, which is not true when compared to what Poh-Shen-Loh wrote and what the problem answer suggests.

• Day 7

  A Cube and a Square Find a Prime 1's and 0's Bonus: Constructing a Set of Nonprimes
  1
  Topics
  1
  Posts

  L

  Since 2021=2025-4=45^2-2^2, which means that 2021 can be written as (45+2)(45-2)=43*47. It's more faster than guessing the numbers and it's more easy to memorize. Although not all numbers can be solved that way

• Day 8

  Mod 17 Find All Solutions Revisiting GCDs
  4
  Topics
  5
  Posts

  S

  @thoughtfulmongoose Let a=2x and b=2y, then the question is asking for the GCD of 2x and 4y. Obviously 2 is a common divisor, but we don't know if x has any more 2s in it. If x has one more factor of 2 and y has none then the greatest common divisor is 4. So the answer should be NEI(not enough info)