 As it happens, this passage is too good to be true: it is almost verbatim what Nicomachus himself wants (see Nicomachus’ Introductio arithmeticae I vi 1, Hoche 1866 p. 12.1–12, D’Ooge et al. 1926 p. 189 e.g.). So it seems best not to ascribe it to Speusippus.