Re: Wall Observer BTC/USD - Bitcoin price movement tracking & discussion
For all we know it could be a reference to the amount of kilotons on the Nagasaki bomb 
https://en.wikipedia.org/wiki/Fat_Man
https://en.wikipedia.org/wiki/Fat_Man
Nah.
Take your pick:
https://www.ridingthebeast.com/numbers/nu21.php
https://www.mastermindcontent.co.uk/the-symbolic-meaning-of-the-number-21/
To me, it represents the “monetary Phoenix” rising from it’s ashes - via ENERGY transformation.
The number 21 is obviously only half of the ultimate answer - which is well known to be 42.