NGC 21

NGC 21 is a spiral galaxy in the Andromeda constellation. It was discovered by German-British astronomer William Herschel on 26 November 1790. Lewis Swift observed it again in 1885, leading to its double listing in the New General Catalogue.

NGC 7831 Group

According to A.M. Garcia, NGC 21 is a member of the NGC 7831 group, which contains at least 18 galaxies, including NGC 13, NGC 19, NGC 20, NGC 39, NGC 43, NGC 7805, NGC 7806, NGC 7819, and NGC 7836.