Unexpected Factorial

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When you use an exclamation mark with a number, you’re actually implying it’s not a normal number any more. It’s a factorial!

Ok, so how does this work?

5!=1×2×3×4×5=120

6!=720

These numbers get really large. For example:

15!≈1.3×10^12

So, next time you see a headline with 2000! in it, you’ll know what to expect.

There are also double factorials (n!!) and iterated factorials (n!)!, and they aren’t the same thing. Just add more exclamation marks and you get multifactorial. Check wikipedia to see how spicy it gets.

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100

51 is divisible by 3! (sh.itjust.works)

submitted 1 month ago by [email protected] to c/[email protected]

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Source: https://lemmy.blahaj.zone/comment/10788469

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[–] [email protected] 1 points 1 month ago* (last edited 1 month ago)

π=3

Source: Mahajan, S. (2014). The art of insight in science and engineering: Mastering complexity. The MIT Press. p. 18.

That page is also a goldmine for of numbers you can use for back of the envelope maths or trolling professionals of various kinds. Are you working with chemists? N_A=6 * 10^23 mol^-1 What about physicists then? c=3 * 10^8 m/s.