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What use are primes?
It's not until your start looking at some really complex stuff like cryptography that prime numbers become useful rather than just "oh wow, cool!" - but we teach kids about them!
So why not teach Abundance? They are a simple enough concept, that's kinda cool to think about and it gets you thinking (and practicing) division, addition, and logic (to an extent).
I haven't knowingly used a prime number since I was introduced to them at school - but every time I go shopping, every site I visit: they are there hiding in the background!
I have no idea if Abundance has a "real world" use - but if it does, then it's probably hidden away in common sight! 
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
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Ironically you mention the most hidden in plain sight one: time.
Hours, minutes, seconds, months all use Abundant numbers.
The imperial system makes extensive use of them.
The idea of using them is there are more divisors, so you can split into more different sized items.
For example 12 can be divided into 2, 3, 4 or 6 but 10 can only be divided into 2 and 5.
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The only reason we use base10 is that we have ten fingers. (Well except for the French and Danes amongst others, no not the number of fingers, but they both partially use base20 in their spoken language)
The Babylonians appreciated abundant numbers and used base60 instead of base10, or the Sexagesimal system, this is where we got our minutes and seconds from.
I don't know why they decided to divide a day into twelve hours instead though. 
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Jörgen Andersson wrote: The only reason we use base10 is that we have ten fingers.
That's why the French use base 20 - they take their socks off to count ...
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Yup, that's it.
Many years ago I recieved a book (actually two tomes) from my brother, "Histoire universelle des chiffres". Luckily a translated version since my French is utterly weak.
An amazing book, but a heavy read that I still haven't finished. 
The first chapters explains probable origins for different bases we have been using throughout history.
Base12 (very common in imperial measures) used the fingerjoints on one hand, excluding the thumb.
Add the thumbs and use both hands and you can count the days of a month.
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Jörgen Andersson wrote: The only reason we use base10 is that we have ten fingers.
I've heard this stated many times but is there any evidence for it?
As we only have unique symbols for the numbers 0 to 9, might it not have been invented by a nine fingered person? (Insert your preferred locale for in-breeding jokes here) - which just happens to work out better for us to do arithmetic.
I've always found it interesting that our system of writing uses a different approach to the way our fingers work. If I want to give someone the sign for ten I'll hold up all ten fingers but to write it down, I have to use a second symbol ("1") followed by an arguably redundant zero, when it could have been "0A" - if we borrow from hex.
Of course, if you used e.g. "A" to represent the number after 9, then you hit all sorts of interesting questions related to zeroes e.g. should it be written "1A" or "20"?
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No proofs but plenty of evidence. 
1) The word for digit comes from the latin word for finger.
B) The roman symbol for 5 is a V which symbolizes a hand, and the symbol for 10 is an X which is two hands.
Interestingly the exeption that the Babylonian sexagesimal system would be, also has symbols for 1-9 and 10-50 and then a new symbol for 60.
There are obviously plenty of exeptions, but the main reason for using base10 is that we have a built in calculator in our hands.
Can recommend reading the book The Universal History of Numbers: From Prehistory to the Invention of the Computer[^] by Georges Ifrah if you're interested.
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Interesting.
Did you happen to see the episode of QI where they claimed that Roman numerals were only very rarely used by the Romans and their popularity is MUCH more recent encouraged by the BBC and others to make dates less readable?
I know nothing of this so merely repeating their claim (they allege it was a BBC policy so that repeated programmes were harder to spot if the date was flashed up quickly in Roman numerals!)
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No, I didn't see it, but if that's the case, what did they use instead?
As far as I understand, roman numerals were pushed away by arabic numerals around 900 AD.
I know they have found Roman Abacuses (Or Abacii? What is the plural actually?) several times that was obviously built according to the roman system. But that doesn't rule out anything.
As so often there could be different system in use in different social layers.
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Sorry, only had it on as "background" and wasn't paying proper attention.
They also said that e.g. four might just as often be written a IIII or IV, similarly VIIII for nine. Both systems were popular.
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Jörgen Andersson wrote: I don't know why they decided to divide a day into twelve hours instead though
Huh, and I thought a day was 24 hours .. Oh well 
Live long and prosper
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Nah, that's a day and a night.
Meanwhile I found an explanation (an explanation, maybe not the explanation)
Apparently the Egyptians divided the day into ten work hours, plus an extra hour each in the morning and the evening for eating and food preparations and stuff.
Haven't a clue if it's correct, but I'll keep looking.
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That isn't a function of those being abundant it's a function of them being highly composite
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Assuming there are 10 people in a train, and 15 of them go out in a train station, 5 must go in at the next station for the train to arrive empty.
Oh nevermind, I read abusing numbers.
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If 5 go in the next station, and 3 decide at the last minute to use the restroom and miss the train, will there be enough people to attend the local town hall, 23.27 year's from now?
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Only if the R value is kept below 1.0
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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Ouch, that's a tough one. 
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Slacker007 wrote: 3 decide at the last minute to use the restroom
You're obviously not from the UK.
The toilets on the stations tend to be owned by Network Rail, and the regional operators save money by not renting them, so they're permanently closed. And even if you're lucky, and happen to be at one of the large stations where they are open, you need to make sure you have the correct change to pay to get in.
Toilets on the trains - on the vanishingly few trains that have them - tend to be permanently out of order. As a result, very few people ever use them, so the PHBs use that to justify saving money on newer trains by not including toilets at all.
Basically, if you're planning to travel by train in the UK, make sure you take an empty bottle with you, since they don't even provide a "toilet-replacement bucket service".
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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When you're a man, the whole world is your restroom.
That's probably why those stations are always so dirty, because these people are learning abundant numbers
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A few years ago I went by train from Manchester airport to Leeds, it was a weird experience that now got an explanation.
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Jörgen Andersson wrote: it was a weird experience that now got an explanation
according to wikipedia "An abundant number which is not a semiperfect number is called a weird number" perhaps that also applies to experiences
I am bemused by quasiperfect numbers...
"An abundant number with abundance 1 is called a quasiperfect number, although none have yet been found"
Live long and prosper
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Richard Deeming wrote: Toilets on the trains
And when they are available, (apart from being awash with assorted bodily fluids) they have electronic doors with no physical lock, and the sliding door opens very wide (to be "accessible") so you spend your time in there in terror of the door randomly and unstoppably opening and exposing your attempts to avoid other people's wee/poo/sick/etc to the entire carriage. (Though these days a large proportion of trains are running almost empty anyway, and I suspect a proportion of the remaining passengers don't even bother looking for the toilet).
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Is the train perfectly frictionless, and the people perfectly spherical?
Asking for a physics friend.
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Of course, and it travels at the speed of light.
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