The hash and the nonce
See https://en.bitcoin.it/wiki/Block_hashing_algorithm to see the code below and a description of the composition of the header
Handout
The block hashing algorithm produces a sha256d hash of 256 bits (32 bytes) based on the following 640 bit input:
Examples
Example python code:
>>> import hashlib
>>> header_hex = ("01000000" +
"81cd02ab7e569e8bcd9317e2fe99f2de44d49ab2b8851ba4a308000000000000" +
"e320b6c2fffc8d750423db8b1eb942ae710e951ed797f7affc8892b0f1fc122b" +
"c7f5d74d" +
"f2b9441a" +
"42a14695")
>>> header_bin = header_hex.decode('hex')
>>> hash = hashlib.sha256(hashlib.sha256(header_bin).digest()).digest()
>>> hash.encode('hex_codec')
'1dbd981fe6985776b644b173a4d0385ddc1aa2a829688d1e0000000000000000'
>>> hash[::-1].encode('hex_codec')
'00000000000000001e8d6829a8a21adc5d38d0a473b144b6765798e61f98bd1d'