Math(s)

[lucaswaffywaf@lemmy.world]

Plz don't groth on my dieck, that's just rude.

[grammarpolice@lemmy.world]

Now provide the proof

[godnroc@lemmy.world]

Or at least not well.

[testfactor@lemmy.world]

Proof Of Divisibility Rules | Brilliant Math & Science Wiki

Divisibility rules are efficient shortcut methods to check whether a given number is completely divisible by another number or not. These divisibility tests, though initially made only for the set of natural numbers ...

(brilliant.org)

The 7 and 13 rules are pretty cool too.

[southsamurai@sh.itjust.works]

Everything is divisible by 17

Only issue is what the result is

[grammarpolice@lemmy.world]

This is insane stuff. 13 is truly mesmerizing. Although I don't think I'm sharp enough for the proofs. Even the divisibility by 2 proof looks hellish.

[prime_minister_keyes@lemm.ee]

Well, on the surface, it's just 60-3, so clearly divisible by 3 itself. Now 221, that's some fuckery.

[brian@lemmy.ca]

You just casually dropping in that 832 is divisible by 8 makes me feel as if there's a small gap in our abilities to do mental math

[juliebean@lemm.ee]

Grothendieck's Prime tripped me up in a maths competition in high school. i had manually stored a list of primes in my calculator, and one of the puzzles involved primes and deducing the combination to a lock from certain clues. my list of primes erroneously included 57, which almost made my team fail the level, until i realized my error.

[yetanotheruser@discuss.tchncs.de]

You are actually allowed to add up infinite series like this.

Only that the infinite series have to be convergent, or else you get little of value. The series in your example oscillates forever (and the oscillation distance remains constant), therefore it diverges.

Take the infinite series 1 + 0 + 0 + 0 + ... and add it like you did:

1 + 0 + 0 + 0 + 0 + ...
___ 1 + 0 + 0 + 0 + ...

And you just get 1 + 1 + 0 + 0 + 0 + ... which is just 2 * (1 + 0 + 0 + 0 + ...)

[hjalamanger@feddit.nu]

Il do it for disability by three and a three digit numbers with the digits a, b and c. The value of that number then is 100a + 10b + c. They concept is the same for nine.

100a + 10b + a mod 3 =
a + b + a

This means that, mod 3, a three digit number is equivalent to the sum of it's digits and therefore preserves disability by 3.

[sudo@lemmy.today]

832 is 800 + 32

800 is obviously divisible by 8, so it can also be negated like the first few digits.
32 is also divisible by 8.

[driving_crooner@lemmy.eco.br]

First step to find 1 + 2 + 3 + ... = -1/12

[zugyuk@lemmy.world]

That's why you always go for multiples of 6 plus or minus 1 that are not multiples of 5 or 11.

[tempermentalanomaly@lemmy.world]

I have discovered a truly marvelous demonstration of this proposition that this comment section is too narrow to contain.

[rebelsimile@sh.itjust.works]

This is how I see it, 30 + 21, doesn’t come up that often obviously, but also we don’t have to love every composite number. In fact, we hates most of them. Add 51 to the pile.

[pfm@scribe.disroot.org]

Reading the beginning of your comment, I was sure you'd end it with "depends how brave you are".

[lennivelkant@discuss.tchncs.de]

Dammit, it was right in the post, why did that take me so long?

[unrepententprocrastinator@lemmy.ca]

All the magic goes when you understand it's 30+21

[vinesnfluff@pawb.social]

"This is called 'maths'. Or 'math' if you're American, as they're only allowed to have one. Due to... I don't know budget cuts or something". — ASHEN, Stuart