code: func DefaultGenesisBlock() *Genesis {
  	return &Genesis{
  		Config:     params.MainnetChainConfig,
  		Nonce:      66,
  		ExtraData:  hexutil.MustDecode("0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa"),
  		GasLimit:   5000,
  		Difficulty: big.NewInt(17179869184),
  		Alloc:      decodePrealloc(mainnetAllocData),
  	}
  }
docs: // DefaultGenesisBlock returns the Ethereum main net genesis block.