# Coins and Maths

I like coins. I’m not a collector. The only coins I have in my possession are the odd foreign euro or dirham from holidays gone by, and a big pile of various UK coins. I’ve never sought a coin in particular, but maybe after this post I will.

I’m focusing, unsurprisingly, on the maths of coins. They come in all sorts of amazing mathematical shapes. I thought I’d show some of them to you. Let’s see how many polygons we can get through. I won’t bother with circles, because duh.

3: The Triangle

There is an Australian \$5 coin! This is not generally circulated currency, but rather a commemorative mint to mark the 25th anniversary of Australian Parliament House. Still, I want one.
Another commemorative mint was this Isle of Man coin celebrating the archeologist Howard Carter
Then there’s this great Reuleaux Triangle coin from Bermuda, which I *think* was general circulated currency.
You may have noticed that the reuleaux triangle is one of the family of shapes of constant width, known collectively as the reuleaux polygons. The twenty pence piece is one too. Many coins are, as they roll nicely in slot machines.

Another commemorative Australian Coin (a squircle!)

The Netherlands (generally circulated):

Poland (commemorative)

I think there was an old Indian Rupee that was square too.

Or how about this rectangular Galapagos \$8 coin? No idea whether this was in circulation or commemorative. You’d think for a teeny place like that… well who knows.

There’s also a rectangular commemorative Korean coin:

5: The pentagon

Slovakia (circulated):

Fiji (commemorative):

6: Hexagonal

Egypt (1940s)

Caribbean (commemorative)

7: Heptagonal

50p (UK)

Falkland Islands:

Aah there’s loads of heptagonal coins. Let’s move swiftly on.

8: Octagonal

Maltese 25 cent coin:

9: Nonagonal

Kenyan 5 shillings:

Austria (commemorative)

10: Decagonal

Belize:

Jamaica:

11: Hendecagonal

We’re learning new words now!

Sri Lanka:

12: Dodecagonal

UK Pound Coin (Coming 2017!)

UK 3 pence (back in the day!)

13: Tridecagonal

Czech Republic:

We’re getting silly now!

Australian (commemorative):

Phew! We’re practically full circle (pun intended).

I can’t find a coin with more sides than this. Can you?

## 2 thoughts on “Coins and Maths”

1. Chris says:

Where’s the dodecagonal Australian 50 cent piece? XD