Definition:Pluperfect Digital Invariant

Definition
Let $n \in \Z_{>0}$ be a positive integer.

$n$ is a pluperfect digital invariant when expressed in decimal notation the $n$th powers of its digits add up to $n$.

Also known as
A pluperfect digital invariant is also known as:
 * a plus perfect number
 * a narcissistic number
 * an Armstrong number.

It is not known who the Armstrong is whose eponym this entry is, although there are rumours that he may have been a Michael Armstrong of Polk City in Florida.