what coin do you have that has the most sides?

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I have a coin from Yemen, km25, that has 21 sides. I wonder, not just theoretically or geometrically, but how many sides can a coin have that is physically or mechanically possible?
I can one up your 21: France KM#856 is reported at having 22 sides.

Beyond some point you'd just get a circle, no? That or reeding.
(There's a Brazilian coin reported as having 24 sides, and a rare token with 29 sides, but I didn't find anything larger.)
By the way, have you noticed about newer coins with sides that they have an uneven number of sides? And do you know why?
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Quote: "Camerinvs"​By the way, have you noticed about newer coins with sides that they have an uneven number of sides? And do you know why?
I don't ​
Vending machines.
Non illegitimis carborundum est.  Excellent advice for all coins.
Make Numismatics Great Again!  
The diameter of a coin with an uneven number of sides is the same wherever you measure it: a peak always faces a side.

When you have an even number of sides the diameter is bigger at the peaks, because peaks face each others, and it is smaller between two peaks. This is not good for the calibrating of vending machines. Interestingly, the Australians have a 12-sided coin, but uneven sides is much more common worldwide.

By the way, the Canadian dollar has 11 sides. I don't think I have any coins with more sides. :(

EDIT: Yes, "vending machines", as pnightingale says.
₱o$₮ag€ $₮am₱$ a₹€ mo₹€ £€₲i₮ima₮€ a$ a ƒo₹m oƒ ¢u₹₹€nc¥ ₮ha₦ ₮h€ €₦₮i₹€ "¢oi₦" ₱₹odu¢₮io₦ oƒ ₦au₹u o₹ ₦iu€. ••• £€$ ₮im฿₹€$-₱o$₮€ $o₦₮ ₱£u$ £é₲i₮im€$ €₦ ₮a₦t qu'o฿j€₮$ mo₦é₮ai₹€$ qu€ £a ₱₹odu¢₮io₦ €₦₮iè₹€ d€ «mo₦₦ai€$» d€ ₦au₹u ou d€ ₦iu€.
Quote: "frankhammer"​I have a coin from Yemen, km25, that has 21 sides. I wonder, not just theoretically or geometrically, but how many sides can a coin have that is physically or mechanically possible?
​On a microscopic level, each of the reeds of a reeded edge would appear as very small "sides." Thus, the limiting factor would be how small the reeds could be made and how large the diameter of the coin could be made.

You might also argue that as the number of sides increases without bound, on a fixed diameter coin, it approaches a round surface. Thus, round coins have an infinite number of sides.
Quote: "Steve27"​​​On a microscopic level, each of the reeds of a reeded edge would appear as very small "sides." Thus, the limiting factor would be how small the reeds could be made and how large the diameter of the coin could be made.

​You might also argue that as the number of sides increases without bound, on a fixed diameter coin, it approaches a round surface. Thus, round coins have an infinite number of sides.

​There is a big difference, though, between a coin that truly has multiple sides and a reeded or round coin, and that's in the way they were conceived. If, for example, you draw a circle with a compass, your intention is not to draw a multi-sided shape... but a circle.

Perhaps we should have a new post in the Free Discussion for all Numista records:

→ coin with the most sides
→ heaviest coin
→ lightest coin (excluding scraps from broken coins)
→ coin with the most writing (likewise medal and token)
→ thickest coin (excluding piedforts)

and so on. Just a fun suggestion...
₱o$₮ag€ $₮am₱$ a₹€ mo₹€ £€₲i₮ima₮€ a$ a ƒo₹m oƒ ¢u₹₹€nc¥ ₮ha₦ ₮h€ €₦₮i₹€ "¢oi₦" ₱₹odu¢₮io₦ oƒ ₦au₹u o₹ ₦iu€. ••• £€$ ₮im฿₹€$-₱o$₮€ $o₦₮ ₱£u$ £é₲i₮im€$ €₦ ₮a₦t qu'o฿j€₮$ mo₦é₮ai₹€$ qu€ £a ₱₹odu¢₮io₦ €₦₮iè₹€ d€ «mo₦₦ai€$» d€ ₦au₹u ou d€ ₦iu€.
It's an interesting topic and one which I'm afraid my meagre understanding can't adequately explain. The issue with even sided coins is that they need more impetus to roll down a modest incline and so they tend to foul the coin chutes on vending macines. I don't quite understand why this is so, I simply accept the wisdom handed down by those who have taken the time to learn such things. But that doesn't mean I'm not curious.

However it's not that simple. A triangular shaped coin is going to have even more problems than a square shaped one despite the odd number of sides and I would hazard a guess that the same holds true for a five sided versus six sided coin. So at some point the angle created by each side has to acheive a certain measure before pyhsics begins to co-operate with the needs of condom dispensers. Does it also depend on the weight of the coin? What impact does it's thickness have? Is there an optimum incline for the coin chute on a vending machine to accomodate all the different types of coins?

Coin making in the 21st century is an exacting science where the needs of durabilty and functionality must be balanced against our human need for beautiful designs. What a pity that this art developed over thousands of years will soon vanish from the face of the Earth.

OK, now I'm depressed. Time for a couple of Vicodin and to buy some coins on eBay with my wife's cerdit card.
Non illegitimis carborundum est.  Excellent advice for all coins.
Make Numismatics Great Again!  
Beside the rolling-down of a coin into a vending machine, there's also, and more importantly I think, the issue of diameter. If you calibrate your machine for an even-sided coin, you have to calibrate for a range of width (let's say, for example, 2.3 to 2.5 cm) that would allow for all kinds of foreign coins in place of the official currency. The problem is that once someone discovers that a cheap foreign coin can be used, people start to know very quickly.

In Canada, until the introduction of the Euro, travelers to France sometimes brought back rolls of French 20 centimes because most vending machines would take such a coin as if it was a 25¢ coin, though it was worth only about 5¢. And indeed two or three times I have received in my change a 20 centimes instead of a 25¢. Now, those two coins have a slightly different diameter, but the owner of vending machines were willing to take the occasional loss rather than to calibrate their slot more tightly, because that would mean that even a lot of 25¢ coins would be rejected as well.

By the way, I suspect that a major advantage of the Australian 12-sided coin I mentioned above is its weight. It's one of the heaviest coins currently circulating in the world, so I suspect tight calibration is less of an issue ─ there's no other coin like it.

Note what the Royal Mint says about the 50p:

While this design may have been traditional, the shape of the new 50p coin, an equilateral curve heptagon, was revolutionary. This made it easily distinguishable from round coins both by feel and by sight, while its constant breadth allowed it to roll in vending machines.

Find out more on their 50p webpage.
₱o$₮ag€ $₮am₱$ a₹€ mo₹€ £€₲i₮ima₮€ a$ a ƒo₹m oƒ ¢u₹₹€nc¥ ₮ha₦ ₮h€ €₦₮i₹€ "¢oi₦" ₱₹odu¢₮io₦ oƒ ₦au₹u o₹ ₦iu€. ••• £€$ ₮im฿₹€$-₱o$₮€ $o₦₮ ₱£u$ £é₲i₮im€$ €₦ ₮a₦t qu'o฿j€₮$ mo₦é₮ai₹€$ qu€ £a ₱₹odu¢₮io₦ €₦₮iè₹€ d€ «mo₦₦ai€$» d€ ₦au₹u ou d€ ₦iu€.
Quote: "Camerinvs"
Quote: "Steve27"​​​On a microscopic level, each of the reeds of a reeded edge would appear as very small "sides." Thus, the limiting factor would be how small the reeds could be made and how large the diameter of the coin could be made.
​​
​​You might also argue that as the number of sides increases without bound, on a fixed diameter coin, it approaches a round surface. Thus, round coins have an infinite number of sides.

​​There is a big difference, though, between a coin that truly has multiple sides and a reeded or round coin, and that's in the way they were conceived. If, for example, you draw a circle with a compass, your intention is not to draw a multi-sided shape... but a circle.

​Perhaps we should have a new post in the Free Discussion for all Numista records:

​→ coin with the most sides
​→ heaviest coin
​→ lightest coin (excluding scraps from broken coins)
​→ coin with the most writing (likewise medal and token)
​→ thickest coin (excluding piedforts)

​and so on. Just a fun suggestion...
​Topology has no intent.
Quote: "Steve27"​​​Topology has no intent.

​Agreed ─and I'm certainly not disagreeing with what you say from that point of view─ but coin designing starts from intent.
₱o$₮ag€ $₮am₱$ a₹€ mo₹€ £€₲i₮ima₮€ a$ a ƒo₹m oƒ ¢u₹₹€nc¥ ₮ha₦ ₮h€ €₦₮i₹€ "¢oi₦" ₱₹odu¢₮io₦ oƒ ₦au₹u o₹ ₦iu€. ••• £€$ ₮im฿₹€$-₱o$₮€ $o₦₮ ₱£u$ £é₲i₮im€$ €₦ ₮a₦t qu'o฿j€₮$ mo₦é₮ai₹€$ qu€ £a ₱₹odu¢₮io₦ €₦₮iè₹€ d€ «mo₦₦ai€$» d€ ₦au₹u ou d€ ₦iu€.
As an English major, I'm always appreciative of encountering new words, and this thread introduced me to two of them:

Icosihenagonal (21-sided) https://en.numista.com/catalogue/pieces4830.html
Icosidigonal (22-sided) https://en.numista.com/catalogue/pieces1161.html

(and I wonder if that French coin used to work in vending machines)
Sounds like organic chem.
also , op should click solved .
Jamais l'or n'a perdu la plus petite occasion de se montrer stupide. -Balzac
Did you ever hear about the Wankel motor used in some cars some years ago?

https://en.wikipedia.org/wiki/Wankel_engine

it worked, but used a lot of oil to keep the combustion tight!
Globetrotter
Coin varieties in French:
https://monnaiesetvarietes.numista.com
We have some interesting ones downunder.
12 Sided coin from Australia Dodecagonal

14 Sided coin from Australia Tetradecagonal

24 Sided coin from Australia - Icositetragonal



This is the edge of the 24 sided coin

Cheers Mike
Referee for Australia & New Zealand Coins & Exonumia, Papua New Guinea & Cocos & Keeling Islands Coins & Australian Banknotes. I Collect > Australia, UK & Dependancies, NZ Sets, USA & Euros plus Misc Exonumia.
I have this coin:

https://en.numista.com/catalogue/pieces9367.html

24 sided coin from Brazil :)
Turi

https://www.instagram.com/my_world_coins_collection
Lol I thought you meant sides as in front and back. I was thinking how does a coin have more than two sides??? Whatever lol.

But I was just wondering... I know that some coins have holes in the middle of them. (Mostly from China and other Asian countries I think) Do the sides on the inside count as sides? It's probably is hard to understand what I am saying without a picture but that was the best way I could explain it. :P

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