Why did Satoshi select 21 Million as the Bitcoin supply?

Does anyone have an idea, why Satoshi selected the Bitcoin fundamentals in a way, to create 21 Million Bitcoin?
Is there something interesting or historical about the number 21?
Or is it because 10 minutes is a round number, 4 years the Government cycle and 50 Bitcoin per block ... just because?

The simple reason for 21 million Bitcoin lies in the 4 variables:

  1. Starting blockreward: 50 Bitcoin
  2. Block frequency: 10 Minutes
  3. Blockreward reduction timing: Every 4 years
  4. Blockreward reduction amount: 1/2
  5. (technically it is not 4 years but a certain amount of blocks, but let's ignore that rounding error)

If you change any of the 4 variables, you get a supply different from 21 million:

1a. Starting blockreward: 25 Bitcoin -> 10.5 Million Bitcoin
1b. Starting blockreward: 100 Bitcoin-> 42 Million Bitcoin

2a. Block frequency: 20 Minutes -> 10.5 Million Bitcoin
2b. Block frequency: 5 Minutes -> 42 Million Bitcoin

3a. Blockreward reduction timing: Every 2 years -> 10.5 Million Bitcoin
3b. Blockreward reduction timing: Every 8 years -> 42 Million Bitcoin

4a. Blockreward reduction amount: 3/4 -> 14 Million Bitcoin
4b. Blockreward reduction amount: 1/4 -> 42 Million Bitcoin

Therefore, why 21 Million? Is there any significance behind it? Has Satoshi ever said anything about that number?

I would also be interested in any ideas or guesses. Very likely noone really knows.

submitted by /u/Knight925 to r/Bitcoin
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Quelle: bitcoin-en