Full Idea
The products of 9 always compose either 9 or some lesser product of 9, if you add the characters of the product. To a superficial observer this regularity appears as chance or design, but a skilful algebraist sees it as necessity.
Gist of Idea
A surprise feature of all products of 9 looks like design, but is actually a necessity
Source
David Hume (Dialogues Concerning Natural Religion [1751], Part 9)
Book Reference
'The Existence of God', ed/tr. Hick,John [Macmillan 1964], p.98
A Reaction
An example of this universal generality is that 369 is a product of 9 (9x41), and if you add 3, 6 and 9 you get 18, which is 2x9. Similar examples occur in nature, such as crystals, which are necessary once the atomic structure is known.