Definition:Pluperfect Digital Invariant/Historical Note

Historical Note on Pluperfect Digital Invariant

The concept of a pluperfect digital invariant was dismissed thus by Godfrey Harold Hardy in his A Mathematician's Apology 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.

Previous to this, they surfaced in Henry Ernest Dudeney's Modern Puzzles of $1926$ as puzzle $94$, although he failed to find $371$.

The eponym of Armstrong number is Michael Frederick Armstrong of Polk City in Florida, a teacher of computing at Rochester University 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.