The elementary theory of numbers should be one of the very best subjects for early mathematical instruction. It demands very little previous knowledge; its subject matter is tangible and familiar; the processes of reasoning which it employs are simple, general and few; and it is unique among the mathematical sciences in its appeal to natural human curiosity. A month’s intelligent instruction in the theory of numbers ought to be twice as instructive, twice as useful, and at least ten times as entertaining as the same amount of “calculus for engineerings.”
Taken from p.818 of his 1929 paper in the Bulletin of the AMS, the text of the sixth Josiah Willard Gibbs Lecture.