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Hallo, new Mastodon users! Here on mathstodon.xyz we've got a couple of mathematical emoji: and . I'd love to add some more. If you can make a PNG image the same size as those, send it to me and I'll add it. Faces of famous mathematicians are an easy place to start; could we have some shapes, polyhedra, or other mathographics too?

A problem of mine appeared in the lastest Mathematics Magazine:

Suppose \(\pi\) is a permutation of \(\{1,2,\ldots,2m\}\). Consider the (possibly empty) subsequence of \(\pi(m+1),\pi(m+2),\ldots,\pi(2m)\) consisting of only those values which exceed \(\max\{\pi(1),\ldots,\pi(m)\}\).

Let \(P(m)\) denote the probability that this subsequence never decreases, when \(\pi\) is a randomly chosen permutation of \(\{1,2,\ldots,2m\}\). Evaluate the limit of \(P(m)\) as \(m\to\infty\).

Mastodon always 'charges' you 23 characters for every URL you post. It doesn't matter if it is longer or shorter.

There is NO excuse for using URL shorteners which obfuscate your destination if you click - these usually go to fb or twitter, so I Never click them on purpose. They make my browser and I feel dirty.

Please tell your friends.

A special Numberphile #video on the mathematical modelling of #Covid19, using the so-called SIR Model. Once again Ben Sparks shows off Geogebra's capabilities.

Also good to see them practising physical distancing!

@christianp There was that Ivory-soap slogan with 100 in the denominator, but I haven't seen that in years.

https://www.straightdope.com/columns/read/870/ivory-soap-is-99-and-44-100-pure-what/

Percentages highlight an often-ignored point about rounding: if you've got a boundary, rounding to it can be very misleading.

For example, if something works 999 of 1000 times, it's not correct to say it's 100% effective. 99% is further from the true value, but shows the existence of the failure.

Or, more thrillingly, are there contexts where numbers are written as decimals, but some decimals are illegal?

This is sometimes true for currencies: a price like £1.054 would normally be rounded to the nearest penny. But if it's a price per unit, you might need that extra digit

Which numbers can you represent with different notations? For example, decimals represent numbers of the form a×10ᵇ, so not even all of ℚ!

What fruity sets can we find a corresponding notation for?

GCompris entertains and educates kids stuck at home. It is available for free for all platforms. Get it here: https://www.gcompris.net/index-en.html

https://www.reddit.com/r/linux/comments/fjad9f/gcompris_entertainseducates_kids_stuck_at_home/

Happy International Day of Mathematics

https://www.mathunion.org/outreach/IDM

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Mathematician, koala fan, mathstodon.xyz admin,

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Joined Apr 2017