The five-cylinder engine is uncommon relative to the ubiquitous four-cylinder, six-cylinder, or eight-cylinder variants. As an odd-number engine, it certainly is in a class of just three such engines.

V4 engines are few and far between(except in motorcycles). It's the reverse situation from 8-cylinder engines, where there are scores of V8s and a count-them-on-one ...

Combustion engines with an odd number of cylinders are not unheard of but are not particularly common, either. Honda‘s just trotted out an interesting one: A V3, so, two pistons on one side and one on ...