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A046075
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Nontrivial undulants; base 10 numbers >100 which are of the form aba, abab, ababa..., where a!=b.
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8
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101, 121, 131, 141, 151, 161, 171, 181, 191, 202, 212, 232, 242, 252, 262, 272, 282, 292, 303, 313, 323, 343, 353, 363, 373, 383, 393, 404, 414, 424, 434, 454, 464, 474, 484, 494, 505, 515, 525, 535, 545, 565, 575, 585, 595, 606, 616, 626, 636, 646, 656
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,1
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REFERENCES
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C. A. Pickover, ``The Undulation of the Monks.'' Ch. 20 in Keys to Infinity. New York: W.H.Freeman, pp. 159-161 1995.
C. A. Pickover, "Wonders of Numbers", Oxford New York 2001, Chapter 52, pp. 123-124, 316-317.
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LINKS
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_Reinhard Zumkeller_, Table of n, a(n) for n = 1..10000
C. A. Pickover, "Wonders of Numbers, Adventures in Mathematics, Mind and Meaning," Zentralblatt review
Eric Weisstein's World of Mathematics, Undulating Number
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PROG
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(Haskell)
import Data.Set (fromList, deleteFindMin, insert)
a046075 n = a046075_list !! (n-1)
a046075_list = f $ fromList $ [10..99] \\ [11, 22, 33, 44, 55, 66, 77, 88, 99]
where f s | m < 100 = f (insert (m * 10 + h) s')
| otherwise = m : f (insert (m * 10 + h) s')
where h = div (mod m 100) 10
(m, s') = deleteFindMin s
-- Reinhard Zumkeller, May 01 2012
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CROSSREFS
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Cf. A046076, A033619.
Sequence in context: A084430 A182693 * A088882 A135602 A095635 A060916
Adjacent sequences: A046072 A046073 A046074 * A046076 A046077 A046078
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KEYWORD
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nonn,base
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AUTHOR
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Eric W. Weisstein
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STATUS
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approved
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