Concept formation programs aim to produce a high yield of concepts which are considered interesting. One intelligent way to do this is to base a new concept on one or more concepts which are already known to be interesting. This requires a concrete notion of the ‘interestingness’ of a particular concept. Restricting the concepts formed to mathematical definitions in finite group theory, we derive three measures of the interestingness of a concept. These measures are based on how much the concept improves a classification of finite groups.