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 A060274 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. 2
 1, 3, 5, 7, 13, 21, 41, 91, 269, 419, 921, 2983, 8519, 18859, 53611, 136631 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 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. This is not correct. See the comment at A099053. - Franklin T. Adams-Watters, Feb 14 2013 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. LINKS C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review EXAMPLE a(11) = 921 because this is the smallest number that requires 11 digits for its expression. CROSSREFS The sequence f(n) is given in A099053. Cf. A060273. Sequence in context: A180450 A051507 A173145 * A005235 A107664 A321671 Adjacent sequences:  A060271 A060272 A060273 * A060275 A060276 A060277 KEYWORD nonn AUTHOR Jason Earls, Mar 22 2001 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 STATUS approved

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Last modified April 23 10:46 EDT 2021. Contains 343204 sequences. (Running on oeis4.)