Norageki!
English name: Five Numbers!
Genres: Mystery, Sci-Fi
Type: OVA, Episodes: 1
Aired: Jan 22, 2011
Studio: Sunrise
Source: Original
Rating: PG-13 - Teens 13 or older
Synopsis:
In an isolated prison, there are only four prisoners and a cat. One day, a power outage opens all the locks and all of the prisoners are released. However, all of the guards are nowhere to be seen and there are no exits. An extraordinary event occurs in response to an old man's strange behavior.

(Source: ANN)