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A060274
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Hard numbers: a(n) = smallest number m with f(m) = n, where f(m) is the smallest number of digits that are needed to construct m using only 1's, 2's and any number of +, -, *, ^ signs, not allowing concatenation of the digits.
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2
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1, 3, 5, 7, 13, 21, 41, 91, 269, 419, 921, 2983, 8519, 18859, 53611, 136631
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| It seems that to obtain this sequence we need to impose the additional rule that x-y is allowed only when x-y > 0.
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REFERENCES
| C. A. Pickover, "Wonders of Numbers", Chapter 78, 'Creator Numbers', Oxford University Press, NY, 2001. pp. 187-189, 343-345.
Ken Shirriff, University of California, personal communication.
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LINKS
| C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review
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EXAMPLE
| a(11)= 921 because this is the smallest number that requires 11 digits for its expression.
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CROSSREFS
| The sequence f(n) is given in A099053. Cf. A060273.
Sequence in context: A180450 A051507 A173145 * A005235 A107664 A085013
Adjacent sequences: A060271 A060272 A060273 * A060275 A060276 A060277
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KEYWORD
| nonn
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AUTHOR
| Jason Earls (zevi_35711(AT)yahoo.com), Mar 22 2001
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EXTENSIONS
| Entry revised by Larry Reeves (larryr(AT)acm.org), Apr 26 2001
Entry improved by comments from Tim Peters (tim.one(AT)comcast.net), Nov 14 2004
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