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A046075 Nontrivial undulants; base 10 numbers >100 which are of the form aba, abab, ababa..., where a!=b. 8
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)
OFFSET

1,1

REFERENCES

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.

LINKS

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

PROG

(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

CROSSREFS

Cf. A046076, A033619.

Sequence in context: A084430 A182693 * A088882 A135602 A095635 A060916

Adjacent sequences:  A046072 A046073 A046074 * A046076 A046077 A046078

KEYWORD

nonn,base

AUTHOR

Eric W. Weisstein

STATUS

approved

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Last modified October 23 00:52 EDT 2014. Contains 248411 sequences.