A219762 Start with 0; repeatedly apply the map {0->012, 1->120, 2->201} to the odd-numbered terms and {0->210, 1->021, 2->102} to the even-numbered terms.

0, 1, 2, 0, 2, 1, 2, 0, 1, 2, 1, 0, 2, 0, 1, 0, 2, 1, 2, 0, 1, 2, 1, 0, 1, 2, 0, 1, 0, 2, 1, 2, 0, 2, 1, 0, 2, 0, 1, 2, 1, 0, 1, 2, 0, 2, 1, 0, 2, 0, 1, 0, 2, 1, 2, 0, 1, 2, 1, 0, 1, 2, 0, 1, 0, 2, 1, 2, 0, 2, 1, 0, 1, 2, 0, 1, 0, 2, 0, 1, 2, 0, 2, 1, 0, 1, 2, 1, 0, 2, 1, 2, 0, 1, 0, 2, 0, 1, 2, 1, 0, 2, 1, 2, 0

Offset: 1

Author

N. J. A. Sloane, Dec 05 2012

Keywords

• nonn

Comments

An infinite squarefree sequence over {0,1,2} that is not generated by a CDOL system.

Examples

			0 -> 012 -> 012021201 -> ...
		

References

• A. Salomaa, Jewels of Formal Language Theory. Computer Science Press, Rockville, MD, 1981, p. 16, Problem 13.

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Programs

Haskell

a219762 = subtract 1 . a099054 . subtract 1
-- Reinhard Zumkeller, Aug 08 2014

Mathematica

f[lst_] := Replace[MapIndexed[{#1, #2[[1]]}&, lst], {{0, n_} :> If[OddQ[n], {0, 1, 2}, {2, 1, 0}], {1, n_} :> If[OddQ[n], {1, 2, 0}, {0, 2, 1}], {2, n_} :> If[OddQ[n], {2, 0, 1}, {1, 0, 2}]}, 1] // Flatten; Nest[f, {0}, 5] (* Jean-François Alcover, Mar 07 2014 *)

Formula

a(n) = A099054(n-1) - 1. - Reinhard Zumkeller, Aug 08 2014