In number theory, a narcissistic number[1][2] (also known as a pluperfect digital invariant (PPDI),[3] an Armstrong number[4] (after Michael F. Armstrong)[5] or a plus perfect number)[6] in a given number base is a number that is the sum of its own digits each raised to the power of the number of digits.
- ^ Weisstein, Eric W. "Narcissistic Number". MathWorld.
- ^ Perfect and PluPerfect Digital Invariants Archived 2007-10-10 at the Wayback Machine by Scott Moore
- ^ PPDI (Armstrong) Numbers by Harvey Heinz
- ^ Armstrong Numbers by Dik T. Winter
- ^ Lionel Deimel’s Web Log
- ^ (sequence A005188 in the OEIS)