Two reasons why there will never be 21M #Bitcoin
1. The last Satoshi will never be mined (see the chart below)
2. The genesis block was hand built, not mined, so the public key attached to the first 50 BTC has no corresponding private key. Therefore, even if Satoshi returns, he cannot spend his first 50 BTC.
real available is ~15M only already known fact 90% r HOARDED not circulating
Round the reward down to 8 digits and it's perfect.
The sum of 1/(2^n) from n equals integers from 0 to infinity is equal to 2. The bitcoin algorithm only goes to 32 because 50/(2^32) = 0.00000001164153... (in 120 years) therefore its not mathatically within reach to mine exactly 21M BTC
