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vampire number

A natural number x that can be factorized as y × z in such a way that the number of occurrences of a particular digit in the representation of x in a given base (say 10) appears the same number of times in the representations in that same base of y and z together. For example, 2187 is a vampire number since 2187 = 21 × 87 ; similarly 136948 is a vampire because 136948 = 146 × 938. Vampire numbers are a whimsical idea that was introduced by Clifford Pickover in 1995. 1


  1. Pickover, Clifford. Keys to Infinity. New York: W. H. Freeman, 1995.

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