This doesn't use a blockchain, it uses a Hashcash-style proof-of-work function (an idea that predates the Bitcoin by decades): https://en.wikipedia.org/wiki/Has

This doesn't use a blockchain, it uses a Hashcash-style proof-of-work function (an idea that predates the Bitcoin by decades): https://en.wikipedia.org/wiki/Hashcash https://en.wikipedia.org/wiki/Hashcash