A number with an Even number of Digits formed by multiplying a pair of -Digit
numbers (where the Digits are taken from the original number in any order) and together. Pairs
of trailing zeros are not allowed. If is a vampire number, then and are called its ``fangs.'' Examples of
vampire numbers include

(Sloane's A014575). There are seven 4-digit vampires, 148 6-digit vampires, and 3228 8-digit vampires. General formulas can be constructed for special classes of vampires, such as the fangs

giving the vampire

where denotes with the Digits reversed (Roushe and Rogers).

Pickover (1995) also defines pseudovampire numbers, in which the multiplicands have different numbers of digits.

**References**

Pickover, C. A. ``Vampire Numbers.'' Ch. 30 in *Keys to Infinity.* New York: Wiley, pp. 227-231, 1995.

Pickover, C. A. ``Vampire Numbers.'' *Theta* **9**, 11-13, Spring 1995.

Pickover, C. A. ``Interview with a Number.'' *Discover* **16**, 136, June 1995.

Roushe, F. W. and Rogers, D. G. ``Tame Vampires.'' Undated manuscript.

Sloane, N. J. A. Sequence A014575 in ``The On-Line Version of the Encyclopedia of Integer Sequences.'' http://www.research.att.com/~njas/sequences/eisonline.html.

© 1996-9

1999-05-26