# vampire number

Consider the integer 1395. In the equation

$$1395=15\cdot 93,$$ |

expressed in base 10, both sides (http://planetmath.org/Equation) use the same digits.

When a number with an even number^{} of digits is also the product of two multiplicands having half as many digits as the product, and together having the same digits, the product is called a vampire number. The multiplicands are called fangs.

By definition, a vampire number can’t be a prime number^{}. But if both of its fangs are prime numbers, then it might be referred to as a “prime vampire number.”

This concept can be applied to any positional base, and to Roman numerals. For example,

$$VIII=II\cdot IV.$$ |

A vampire number is automatically a Friedman number also.

Title | vampire number |
---|---|

Canonical name | VampireNumber |

Date of creation | 2013-03-22 15:45:10 |

Last modified on | 2013-03-22 15:45:10 |

Owner | CompositeFan (12809) |

Last modified by | CompositeFan (12809) |

Numerical id | 8 |

Author | CompositeFan (12809) |

Entry type | Definition |

Classification | msc 11A63 |

Defines | vampire number |

Defines | fang |