An Armstrong number (named so after Michael F. Armstrong), also called a narcissistic number, a pluperfect digital invariant, or a plus perfect number, is a number that is equal to the sum of its own digits when they are raised to the power of the number of digits. As an example, the smallest Armstrong number is 153, which is equal to 
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To determine if a number with three digits is a narcissistic number, you must first determine its digits in order to sum their powers. However, this involves division and modulo operations, which are expensive. A much faster way to compute it is to rely on the fact that a number is a sum ...
