According to the Yellow Paper, the genesis block is specified by 15 items as follows:
KEC((42)), it goes on to say:
KEC (42) refers to the Keccak hash of a byte array of length one whose first and only byte is of value 42, used for the nonce.
The question is, does this have a practical purpose?
My conjecture is that it's a whimsical reference to Douglas Adams's 1978 novel <<The Hitchhiker's Guide to the Galaxy>>.