Then how many of the bitcoins were put out in the Blockchain from the onset by Satoshi. I always thought it's 21million and these is quite different from the number of blocks . Aren't they?
0, Satoshi started Bitcoin with no Bitcoins.
The distribution mechanism of Bitcoin is actually dictated by halving itself. Satoshi used a base of 50 Bitcoins and halved it for every 210,000 blocks. The distribution of Bitcoin's supply would be a geometric progression with a ratio of 0.5. If you use the formula to calculate the limit of it, you will get approximately 21 Million, but not exactly. As such, there will actually be less than 21 million Bitcoin in existence in the future.