Didymus the Blind stands within the tradition of Alexandrian biblical interpretation, a tradition which can be traced to Philo. Didymus mentions the name of Philo more than any Alexandrian exegete before him, and specifically references Philo's interest in arithmological exegesis. In this paper I propose to discuss arithmology in Philo and Didymus, and to outline the influence of the former on the arithmological exegesis of the latter.