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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 21 × 6000 or 210 × 600) is not, as 21 and 6000 do not have the correct length, and both 210 and 600 have trailing zeroes. Similarly, 1023 (which can be expressed as 31 × 33) is not, as 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, ... There are many known sequences of infinitely many vampire numbers following a pattern, such as: : 1530 = 30×51, 150300 = 300×501, 15003000 = 3000×5001, ... ==Multiple fang pairs== A vampire number can have multiple distinct pairs of fangs. The first of infinitely many vampire numbers with 2 pairs of fangs: :125460 = 204 × 615 = 246 × 510 The first with 3 pairs of fangs: :13078260 = 1620 × 8073 = 1863 × 7020 = 2070 × 6318 The first with 4 pairs of fangs: :16758243290880 = 1982736 × 8452080 = 2123856 × 7890480 = 2751840 × 6089832 = 2817360 × 5948208 The first with 5 pairs of fangs: :24959017348650 = 2947050 × 8469153 = 2949705 × 8461530 = 4125870 × 6049395 = 4129587 × 6043950 = 4230765 × 5899410 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「vampire number」の詳細全文を読む スポンサード リンク
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