Number of transactions in block why sometimes block has 16 transactions and sometimes over 2000?
I checked it on https://blockexplorer.com/blocks.
Thank you
Since the block size is fixed (but has changed since genesis block) there are 2 main reasons:


Transactions are not all the same size in bytes. One transaction can have multiple inputs and outputs, increasing the size of the tx in bytes.
The market might not fill a block with transactions (esp. in the beginning blocks) because usage is low.