It's not intuitive, but the first four bytes (eight hex characters) of the block_id are the block number. Just take the first eight chars of it and unhexlify it to an int and that's the block number.

Basically, all the blocks IDs are a zero-padded blocknum + the block's hash.

This means that the block IDs sort sequentially when sorted lexicographically, which is not a property that most block identifiers have on other blockchains, being randomly distributed within the hash space.