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A033619 Undulating numbers (of form abababab... in base 10). 10
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: A001477 A087156 A254109 * A130734 A258069 A244581

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 August 28 18:07 EDT 2015. Contains 261154 sequences.