A twin dub is a dub number that differs from another dub number by two in any base, for example the twin dub pair in base10 (99, 100). Sometimes the term twin dub is used for a pair of twin dubs; an alternative name for this is dub twin or dub pair.
The ``twin dubs of order k in base b'', denoted ㎎(k,b), where k is a natural number {1,2,3...∞} and b the base.