What concepts or facts do you know from math that is mind blowing, awesome, or simply fascinating?

Here are some I would like to share:

  • Gödel’s incompleteness theorems: There are some problems in math so difficult that it can never be solved no matter how much time you put into it.
  • Halting problem: It is impossible to write a program that can figure out whether or not any input program loops forever or finishes running. (Undecidablity)

The Busy Beaver function

Now this is the mind blowing one. What is the largest non-infinite number you know? Graham’s Number? TREE(3)? TREE(TREE(3))? This one will beat it easily.

  • The Busy Beaver function produces the fastest growing number that is theoretically possible. These numbers are so large we don’t even know if you can compute the function to get the value even with an infinitely powerful PC.
  • In fact, just the mere act of being able to compute the value would mean solving the hardest problems in mathematics.
  • Σ(1) = 1
  • Σ(4) = 13
  • Σ(6) > 101010101010101010101010101010 (10s are stacked on each other)
  • Σ(17) > Graham’s Number
  • Σ(27) If you can compute this function the Goldbach conjecture is false.
  • Σ(744) If you can compute this function the Riemann hypothesis is false.

Sources:

  • backseat@lemmy.world
    27·
    1 year ago

    The square of any prime number >3 is one greater than an exact multiple of 24.

    For example, 7² = 49= (2 * 24) + 1

    • Thoth19@lemmy.world
      7·
      1 year ago

      Does this really hold for higher values? It seems like a pretty good way of searching for primes esp when combined with other approaches.

      • metiulekm@sh.itjust.worksEnglish
        5·
        1 year ago

        Every prime larger than 3 is either of form 6k+1, or 6k+5; the other four possibilities are either divisible by 2 or by 3 (or by both). Now (6k+1)² − 1 = 6k(6k+2) = 12k(3k+1) and at least one of k and 3k+1 must be even. Also (6k+5)² − 1 = (6k+4)(6k+6) = 12(3k+2)(k+1) and at least one of 3k+2 and k+1 must be even.

    • manishmehra@lemmy.ml
      11·
      1 year ago

      I don’t get it,

      5² = 25 != (2 * 24) + 1

      11² = 121 != (2 * 24) + 1

      Could you please help me understand, thanks!

      • msage
        3·
        1 year ago

        Not 2 * 24, but x * 24.

        So 5^2 = 1 * 24 +1

        11^2 = 5 * 24 + 1