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A033619 Undulating numbers (of form abababab... in base 10). 9
0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 101, 111, 121, 131, 141, 151 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

REFERENCES

C. A. Pickover, "Keys to Infinity", Wiley 1995, p. 159,160.

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

MATHEMATICA

wave[1] = Range[0, 9]; wave[2] = Range[10, 99]; wave[n_] := wave[n] = Select[ Union[ Flatten[ {id = IntegerDigits[#]; FromDigits[ Prepend[id, id[[2]]]], FromDigits[ Append[id, id[[-2]]]]} & /@ wave[n-1]]], 10^(n-1) < # < 10^n & ]; Flatten[ Table[ wave[n], {n, 1, 3}]] (* Jean-Fran├žois Alcover, Jun 19 2012 *)

PROG

(Haskell)

import Data.Set (fromList, deleteFindMin, insert)

a033619 n = a033619_list !! (n-1)

a033619_list = [0..9] ++ (f $ fromList [10..99]) where

   f s = m : f (insert (m * 10 + h) s') where

     h = div (mod m 100) 10

     (m, s') = deleteFindMin s

-- Reinhard Zumkeller, May 01 2012

CROSSREFS

Sequence in context: A000027 A001477 A087156 * A130734 A090108 A090109

Adjacent sequences:  A033616 A033617 A033618 * A033620 A033621 A033622

KEYWORD

nonn,base,easy

AUTHOR

N. J. A. Sloane.

STATUS

approved

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Last modified July 29 00:19 EDT 2014. Contains 245011 sequences.