Definition:Pluperfect Digital Invariant/Historical Note

Historical Note on Pluperfect Digital Invariant
The concept of a pluperfect digital invariant was dismissed thus by in his  of $1940$:


 * There are just four numbers, after unity, which are the sums of the cubes of their digits: $153=1^3+5^3+3^3$, $370=3^3+7^3+0^3$, $371=3^3+7^3+1^3$, and $407=4^3+0^3+7^3$. These are odd facts, very suitable for puzzle columns and likely to amuse amateurs, but there is nothing in them which appeals to the mathematician.

The eponym of Armstrong number is  of Polk City in Florida, a teacher of computing at in the $1960$s.

He set as an assignment an exercise to hunt for them.

While the concept did not originate with him, his name can often be seen associated with them.