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Consider the integer 1395. In the equation
expressed in base 10, both sides 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 even to Roman numerals. For example,
A vampire number is automatically a Friedman number also.
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