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| Consider the integer 1395. In the equation $$1395 = 15 \cdot 93,$$ expressed in base 10, both \PMlinkname{sides}{Equation} use the same digits. |
Consider the integer 1395. In the equation $$1395 = 15 \cdot 93,$$ expressed in base 10, both \PMlinkname{sides}{Equation} use the same digits. |
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| 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 {\em vampire number}. The multiplicands are called {\em fangs}. |
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 {\em vampire number}. The multiplicands are called {\em fangs}. |
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| 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.'' |
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.'' |
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| This concept can be applied to any positional base, and even to Roman numerals. For example, $$VIII = II \cdot IV.$$ |
This concept can be applied to any positional base, and even to Roman numerals. For example, $$VIII = II \cdot IV.$$ |
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| A vampire number is automatically a Friedman number also. |
A vampire number is automatically a Friedman number also. |
