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Petri Laarne

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Hi! I'm a maths student at Helsinki University. For the past year or so I've been writing a popular (not as in visitors) maths blog,, in Finnish. In addition to human languages (FIN/ENG/SWE/FRE) I respond to quite a few computer ones (esp. C#).

Interested in seeing if toots > tweets!

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Just finished Jordan Ellenberg's How Not to Be Wrong. Good mix of theory + rhetoric, touches on some hot issues, and imparts several important moral lessons.

A little spoilery: the book indeed suggests ways to not be wrong using mathematical lenses, but cleverly doesn't promise "ways to be right" 😉

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@JordiGH In fact it's based on a lovely result from the 1930's, way before the probability arguments become common in combinatorics.

CC: @petrilaarne

I quite liked @ColinTheMathmo’s entry to : a simple, initially counterintuitive result that becomes intuitively obvious after a quick think! I wonder how many totally different ways there are to prove it.

If you haven’t yet, go read about it and beautiful Penrose tilings:

I’m amazed that I managed full six weeks before messing up my repository at work.

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So, how many of you call the # symbol the hashtag in all contexts, like you would call . period or dot or you @ the at?

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I'm running a four-round instant knock-out tournament throughout the month of July to basically squeeze a load of fun maths out of my friends. Let's see if we can make it all come together! Voting starts on the 1st of July.

I’ve now updated the original post with a solution. Hoping that we found the same one!

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being an applied mathematician means praying to every religious figure that your code converges

Correction: 18D should read ”Each digit is the last digit of twice the preceding digit”. Thanks @christianp for spotting this! (And very ace to solve a puzzle with an error in it 😎)

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When designing a user interface, imagine some old woman using it, say Margaret Hamilton, and she's clicking your app's buttons and saying to you, as old people do,

"Young whippersnapper, when I was your age, I sent 24 people to the ACTUAL MOON with my software in 4K of RAM and here I am clicking your button and it takes ten seconds to load a 50 megabyte video ad and then it crashes

I'm not even ANGRY with you, I'm just disappointed."

If you fancy a bit bigger but not too difficult , I just published a on my blog! I promise it’s much easier than the Magazine one.

It is also very humbling to work in a team of so many PhD’s. My interpretation of ”fun algorithm work” is pretty lame compared to what they do! Still, very encouraging to see how much I already can do.

I guess I should mention that I started a couple weeks ago as a summer intern at , working on dose planning software. That’s very exciting, especially as barely a BSc student! Can’t comment on specifics, but doing fun algorithm work, applying for good.

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math puzzle, link Show more

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"Remember! Most strings are incompressible, most reals uncomputable, most theorems unprovable, most programs undecidable."

― Gwern

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to comply with GDPR, as of May 25th, I will no longer be remembering anybody’s name, face or personal details without their explicit consent

...phew, finally a viable excuse

Just had the last exam of the year, and the sky’s not too bad either. I approve!

Things you can do in : attend the grand opening of grazing season at the university research farm! 🐄🐄 (I’m not sure whether this is ridiculous or amazing for a capital city.)

Re today’s (, my compromise between ”lay-tecks” and ”lah-tekh” is ”late ex”. *ducks*

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Recently I discovered a surprising fact about numbers, so I made an online web thing to give it the recognition it deserves. Give it a go:
A little write-up on @aperiodical at