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Search: id:A060391
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| A060391 |
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If 10^n can be written as x*y where the digits of x and y are all nonzero, then let a(n) = largest such y, otherwise a(n) = -1. |
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2
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| 1, 5, 25, 125, 625, 3125, 15625, 78125, -1, 1953125, -1, -1, -1, -1, -1, -1, -1, -1, 3814697265625, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 116415321826934814453125, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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According to Ogilvy and Anderson, 10^33 is the highest known power of ten that can be expressed as the product of two zero-free factors. "If there is another one, it is greater than 10^5000." p. 89
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REFERENCES
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C. Stanley Ogilvy and John T. Anderson, Excursions in Number Theory, Oxford University Press, 1966, p. 89.
Rudolph Ondrejka, Nonzero factors of 10^n, Recreational Mathematics Magazine, no. 6 (1961), p. 59.
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EXAMPLE
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10^2 = 4 * 25, so a(2) = 25.
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CROSSREFS
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Cf. A060376 (for values of x).
Sequence in context: A132839 A129066 A102169 this_sequence A000351 A050735 A083590
Adjacent sequences: A060388 A060389 A060390 this_sequence A060392 A060393 A060394
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KEYWORD
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sign
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Apr 02 2001
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