Vampire number: an even-digit number n = f₁ × f₂ where f₁,f₂ (fangs) each have half the digits, and the digits of f₁f₂ are a permutation of n's digits. Not both fangs end in 0. First: 1260=21×60, 1395=15×93, 1435=35×41, 1530=30×51, 1560=39×40.
How to Use
Enter number:
- Vampire?: Has valid fangs?
- Fangs: The factor pair(s)
- Type: True vs pseudo
Rules
1. n has 2k digits. 2. Fangs each have k digits. 3. Digits of fangs = permutation of n's digits. 4. At most one fang ends in 0. Some vampires have multiple fang pairs: 125460 = 204×615 = 246×510.
Counting
4-digit vampires: 7 (1260-6880). 6-digit: 148. 8-digit: thousands. Growth is rapid. No formula for the n-th vampire number exists.
Step-by-Step Instructions
- 1Enter number.
- 2Check vampire.
- 3View fangs.
- 4Classify type.
- 5Browse vampires.