This is a proof that enough computational resources have been spent in order to build a valid block. PoW is based on the idea that a random node is selected every time to create a new block. In this model, nodes compete with each other in order to be selected in proportion to their computing capacity. The following equation sums up the PoW requirement in bitcoin:
H ( N || P_hash || Tx || Tx || . . . Tx) < Target
Where N is a nonce, P_hash is a hash of the previous block, Tx represents transactions in the block, and Target is the target network difficulty value. This means that the hash of the previously mentioned concatenated fields should be less than the target hash value.
The only way to find this nonce is the brute ...
