In mathematics, a vampire number (or true vampire number) is a composite natural number v, with an even number of digits n, that can be factored into two integers x and y each with n/2 digits and not both with trailing zeroes, where v contains precisely all the digits from x and from y, in any order, counting multiplicity. x and y are called the fangs.
For example: 1260 is a vampire number, with 21 and 60 as fangs, since 21 × 60 = 1260. However, 126000 (which can be expressed as 210 × 600) is not, as both 210 and 600 have trailing zeroes. Similarly, 1023 (which can be expressed as 31 × 33) is not, because although 1023 contains all the digits of 31 and 33, the list of digits of the factors does not coincide with the list of digits of the original number.
Vampire numbers first appeared in a 1994 post by Clifford A. Pickover to the Usenet group sci.math, and the article he later wrote was published in chapter 30 of his book Keys to Infinity.
The vampire numbers are:
1260, 1395, 1435, 1530, 1827, 2187, 6880, 102510, 104260, 105210, 105264, 105750, 108135, 110758, 115672, 116725, 117067, 118440, 120600, 123354, 124483, 125248, 125433, 125460, 125500, ... (sequence A014575 in OEIS)
There are many known sequences of infinitely many vampire numbers following a pattern, such as:
- 1530 = 30×51, 150300 = 300×501, 15003000 = 3000×5001, ...
Read more about Vampire Number: Multiple Fang Pairs, Variants
Famous quotes containing the words vampire and/or number:
“If I’ve killed one man, I’ve killed two—
The vampire who said he was you
And drank my blood for a year,
Seven years, if you want to know.”
—Sylvia Plath (1932–1963)
“If I could live as a tree, as a river, as the moon, as the sun, as a star, as the earth, as a rock, I would. ...Writing permits me to experience life as any number of strange creations.”
—Alice Walker (b. 1944)