According to the Yellow Paper, the genesis block is specified by 15 items as follows:

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Regarding 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>>.

2 Answers 2


No, it doesn't have a practical purpose. That value is assigned to the nonce field. It is used as part of the proof of work to generate a valid block.

Miners assign different values to that field and compute the block proof of work, if the result is below the difficulty of the network they submit the block to claim the block reward.

But beyond that it has no other purpose.


42 and Pi are popular magic numbers in Ethereum :)

  • As well as 69
    – Lsaether
    Mar 30, 2018 at 17:58

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