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 A033619 Undulating numbers (of form abababab... in base 10). 11
 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 MAPLE \$0..9, seq(seq(seq(a*(10^(d+1)-10^(d+1 mod 2))/99 + b*(10^d - 10^(d mod 2))/99, b=0..9), a=1..9), d=2..6); # Robert Israel, Jul 08 2016 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-François 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 Cf. A016073, A122875, A242541. Sequence in context: A292579 A262530 A291179 * A130734 A118759 A258069 Adjacent sequences:  A033616 A033617 A033618 * A033620 A033621 A033622 KEYWORD nonn,base,easy AUTHOR STATUS approved

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Last modified October 19 04:40 EDT 2019. Contains 328211 sequences. (Running on oeis4.)