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Problem of the Week 1135
A "vampire number" is an integer with 2n digits that is the product of two n-digit numbers — the fangs — whose digits, when combined, form a permutation of the original digits (thus, multiplicity counts). The smallest vampire numbers are
Technical point: The fangs cannot each end in a 0. So 126000 is not a vampire number.
You might have missed it, but October 5, 2010, was a vampire day because
When is the next vampire day?
What is the first double vampire number? In other words, what is the first number having two different factorizations into fangs,
Source: Ed Pegg's blog.
© Copyright 2010 Stan Wagon. Reproduced with permission.