Ehrenfels’ core idea in Das Primzahlengesetz is to apply the notion of Gestalt to number series to find the law-like regularities in the distribution of prime numbers. Therefore Ehrenfels decided to include the entire text of his 1890 article “Über Gestaltqualitäten” in the work, unchanged, though split into two parts. In the course of his discussion, Ehrenfels once again goes down the familiar road of Brentanist mathematics: a discussion of proper and symbolic presentations of number, the limits of our presentational capacity, proper number conceptions as based on (higher order) relations of distinction, etc. (Ehrenfels 1922, 30 ff.) He explicitly considers the proper number presentations as Gestalt qualities, and to be precise, as presentations of “second order”. Collections of numbers, which he calls Zahlenfiguren, would be of third order. These number figures play a central role in, literally, “figuring out” the prime numbers: by generating series of number figures corresponding to all multiples of a base number, which can then be combined in such a way as to filter out the primes.