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A018856
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2^a(n) is smallest power of 2 beginning with n.
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6
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0, 1, 5, 2, 9, 6, 46, 3, 53, 10, 50, 7, 17, 47, 77, 4, 34, 54, 84, 11, 31, 51, 61, 81, 8, 18, 38, 48, 68, 78, 98, 5, 25, 35, 45, 55, 75, 85, 95, 12, 22, 32, 42, 145, 52, 62, 72, 82, 92, 102, 9, 19, 29, 39, 142, 49, 59, 162, 69, 79, 89, 192, 99, 6, 16, 119, 26, 36, 139, 46, 149, 56, 66
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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REFERENCES
| A. M. & I. M. Yaglom, Challenging Mathematical Problems With Elementary Solutions, Vol. 1 pp. 29;199-200 Prob. 91a Dover NY 1987
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LINKS
| Daniel Mondot, Table of n, a(n) for n=1..32699
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MATHEMATICA
| f[n_] := Block[{k = 1, m = Floor[ Log[10, n]]}, While[ Log[10, 2^k] < Floor[ Log[10, n]], k++ ]; While[ Quotient[2^k, 10^(Floor[k*Log[10, 2]] - m)] != n, k++ ]; k]; f[1] = 0;; Array[f, 73] [From Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 02 2009]
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PROG
| (Haskell)
import Data.List (isPrefixOf, findIndex)
import Data.Maybe (fromJust)
a018856 n =
fromJust $ findIndex (show n `isPrefixOf`) $ map show a000079_list
-- Reinhard Zumkeller, Aug 04 2011
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CROSSREFS
| Cf. A018802.
A100129: a(n)=n. [From Robert G. Wilson v (rgwv(AT)rgwv.com), Jun 02 2009]
Cf. A030000, A000079.
Sequence in context: A188933 A177345 A180726 * A019093 A097897 A063761
Adjacent sequences: A018853 A018854 A018855 * A018857 A018858 A018859
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KEYWORD
| nonn,base
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AUTHOR
| David W. Wilson (davidwwilson(AT)comcast.net)
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