Gregory simply multiplies 17 by 3 and again by 3 (i.e., 17 x 32), and thus arrives at 153. Augustine, on the other hand, employs addition, and takes the sum of all the digits to and including 17 as amounting to exactly 153. He says:
For if you add 2 to 1, you have 3, of course; if to these you add 3 and 4, the whole number makes 10; and then if you add all the numbers that follow up to 17, the whole amounts to the aforesaid number [153]; that is, if to 10, which you had reached by adding all together from 1 to 4, you add 5, you have 15; to these add 6, and the result is 21; then add 7, and you have 28; to this add 8, and 9, and 10, and you get 55; to this add 11, and 12, and 13, and you have 91; and to this again add 14, and 15, and 16, and it comes to 136; and then add to this the remaining number of which we have been speaking, namely 17, and it will make up the number of fishes. (Tract. in Ioh. 122, ed. Ben. 3, 813-14)
We should express this, now, more scientifically, and say, 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 +14 + 15 + 16 + 17 = 153. And Gregory's we should express thus: (10 + 7) x (3 x 3) = 153.
Anyway, thank's Joanna. This helps demonstrate that the idea that the Christian fish (= 50 in Hebrew) was recognized in antiquity to have an association with Pythagoreanism.
