The term "human computer" has been recently used by a group of researchers who refer to their work as "human computation". In this usage, "human computer" refers to activities of humans in the context of human-based computation (HBC) - wikipedia 
Leonhard Euler was a prominent mental calculator - - wikipedia
This usage is questionable for the following reason. HBC is a computational technique where a machine outsources certain (not necessarily algorithmic) tasks to humans. In fact, most of the time humans in the context of HBC are not provided with a sequence of exact steps that needs to be executed to yield an answer. HBC is agnostic about how humans solve the problem. This is why the term outsourcing is used in the definition. The use of humans as "human computers" in the context of HBC is very rare.