Why are there 21 million bitcoins?

When all mining is done, there will be a maximum of 21 million bitcoins in circulation. Why was this number chosen? My speculation: 21 million was chosen to ensure a sensible smallest unit if Bitcoin were the world’s exclusive currency.

The real unit of Bitcoin is not the bitcoin; it is the satoshi: the satoshi is the unit used in transactions, and it is indivisible. There will be 2.1e15 satoshis in circulation. The indivisible unit in USD is the cent; it’s not really possible to sell items for fractions of a cent. There are about 6e15 cents in circulation today (across all currencies). Thus if everyone used Bitcoin, the satoshi would be worth about 3 cents, which the world has decided is a sensible minimum amount.

At this time, 1 BTC would be worth $2,800,000.

What can computers do? What are the limits of mathematics? And just how busy can a busy beaver be? This year, I’m writing Busy Beavers, a unique interactive book on computability theory. You and I will take a practical and modern approach to answering these questions — or at least learning why some questions are unanswerable!

It’s only $19, and you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

After months of secret toil, I and Andrew Carr released Everyday Data Science, a unique interactive online course! You’ll make the perfect glass of lemonade using Thompson sampling. You’ll lose weight with differential equations. And you might just qualify for the Olympics with a bit of statistics!

It’s $29, but you can get 50% off if you find the discount code ... Not quite. Hackers use the console!

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