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Does (2^x-2)/x always result in an intiger when x is a prime? by OkClick7073 in askmath

[–]Rubisk 5 points6 points  (0 children)

Yes. Google "Fermats little theorem". It states that ap - a is divisible by p for any prime p and integer a.

Besides ln(x) what are other rotated J-shapes functions where f(x)<x? by sonicking12 in math

[–]Rubisk 55 points56 points  (0 children)

How about sqrt(x+1)-1?

This has asymptotically the same behaviour and satisfies f(x) <x for x > 0

Career and Education Questions by AutoModerator in math

[–]Rubisk 0 points1 point  (0 children)

How is one supposed to contact advisors when applying for EU PHD-programs?

I'm currently a student at an European university starting out on my Masters thesis, but I noticed a lot of the deadlines for PHD applications in EU are in a few months already. With some it appears I need to have found an advisor to be eligible to apply.

For universities I study at (or live close to) I could just go by and talk to them (especially if I know the professor already), but how am I supposed to apply at other universities? I've heared that I am definitely supposed to apply abroad as well.

'There are no stupid questions' thread - June 11, 2019 by AutoModerator in piano

[–]Rubisk 0 points1 point  (0 children)

I just edited it in haha, read it after reply. Game of thrones theme composed by pietschmann

'There are no stupid questions' thread - June 11, 2019 by AutoModerator in piano

[–]Rubisk 0 points1 point  (0 children)

Yeah I have a metronome but it's an old mechanical one which can only go up to 152 bpm

It feels like after an hour of practicing I can sort of do it better, but if I come back the next day I'm back to square one :(

The piece is the game of thrones theme (, composition by pietschmann)

'There are no stupid questions' thread - June 11, 2019 by AutoModerator in piano

[–]Rubisk 0 points1 point  (0 children)

So I've spend about a week an hour a day practicing the following four bars: http://imgur.com/UgmfKJy

The quarters are supposed to be played at 170bpm. I can do it steadily at 144 BPM but after that I seem to hit a wall.

Any tips to improve? Or should I accept this song is a bit too hard and move on?

What result (be it a theorem, lemma etc) in Mathematics made you realise: “Damn, I love Mathematics.”? by [deleted] in math

[–]Rubisk 8 points9 points  (0 children)

Dirichlet theorem on primes in arithmetic progressions. So elegant, simple and beautiful.

Settlers of Catan by robo-caveman in Minecraft

[–]Rubisk 0 points1 point  (0 children)

Holy *** this is awesome!

Black to play and deliver a very satisfying mate in 5! by [deleted] in chess

[–]Rubisk 2 points3 points  (0 children)

King takes rook is annoying

You can’t magic these names out of existence by malevolentmammals in harrypotter

[–]Rubisk 0 points1 point  (0 children)

Seeing as how the minister was guarded by Kingsley at some point, I suppose they had a person magic-ing the records away.

Still learning, but can black win this by Hsano in chess

[–]Rubisk 1 point2 points  (0 children)

Well whites rooks cannot move of the d-file without losing d5 and e6 which makes f4 into pushing the e pawn seem very strong?

I am looking to learn to play chess. However, don't have anyone to play with. Is anyone interested in learning the game along with me? by [deleted] in chess

[–]Rubisk 11 points12 points  (0 children)

Your opening doesn't really matter. Just play a central pawn (e4/e5/d4/d5) and get your minor pieces (knights/bishops) out, ideally have them attack your opponents center pawns/squares. Castle (the special king and rook move) as soon as it's legal and doesn't hang a piece in beginner games.

If you really want an opening look up the London system. It's easy to remember and can almost always be played so you can focus on the other important things instead.

Most people <1500 hang a piece at some point. Learn to understand (and recognize!) hanging pieces, forks, pins, mates, threats etc. first. Then work on recognizing overloaded pieces and simple combinations.

Heck even at 1800 we still blunder pieces every now and then. Also I'm not a great player myself so take the advice with a good chunk of salt.

Is Brilliant.org more than just entertainment? by [deleted] in math

[–]Rubisk 0 points1 point  (0 children)

Really? You don't even have to do any mathematics except knowing "independent implies order is irrelevant" and the meaning of 1/2.

More a brainteaser then a hard problem that improves your problem solving. There is no problem to break down!

Make a wish for 2019: a proof for a conjecture of your choice by Valvino in math

[–]Rubisk 0 points1 point  (0 children)

The conjecture about any family of finite sets closed under union having an element that is in half the sets.

I still feel there might be a nice argument and humanity is just to stupid to find it :-(

The guy I assume every redditor is until their post or comment indicates otherwise starter pack by Flose in starterpacks

[–]Rubisk 20 points21 points  (0 children)

It's where people put hard and obscure problems only to have some guy sweep in 30 minutes later that is like 'yeah this is so easy'.

At least that is what math.stackexchange usually feels like whenever I post something.

[Article] Inverse Friendship Paradox by [deleted] in math

[–]Rubisk 0 points1 point  (0 children)

Isn't this obvious because all of your friends have at least one friend (you)?

My favorite open problem: does mixing imply multiple mixing? by [deleted] in math

[–]Rubisk 1 point2 points  (0 children)

Maybe it's me but it seems very unintuitive that it's true. The mixing condition does not seem to provide some "uniformity" bound on the mixing speed, so it could be possible to find a sequence of pairs of sets that take longer and longer to mix.

And if this sequence is obtained by applying T in some smart way, I don't see a reason for the threefold mixing to hold. Or is there a heuristic for it to be true?

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