Pluperfect Digital Invariant/Examples/3 Digits/Historical Note

Historical Note on $3$-Digit Pluperfect Digital Invariants
In the words of in his  of $1940$:
 * These are odd facts, very suitable for puzzle columns and likely to amuse amateurs, but there is nothing in them that appeals to the mathematician. The proofs are neither difficult nor interesting -- merely a little tiresome. The theorems are not serious; and it is plain that one reason ... is the extreme speciality of both the enunciations and the proofs, which are not capable of any significant generalization.