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A170823 An infinite word on the alphabet 1, 2, 3 in which no block appears twice in succession. 0
1, 2, 3, 2, 1, 2, 3, 1, 3, 2, 3, 1, 2, 1, 3, 2, 3, 1, 3, 2, 1, 2, 3, 2, 1, 2, 3, 1, 3, 2, 3, 1, 2, 1, 3, 1, 2, 3, 2, 1, 3, 1, 2, 1, 3, 2, 3, 1, 3, 2, 3, 1, 2, 1, 3, 1, 2, 3, 2, 1, 2, 3, 1, 3, 2, 1, 2, 3, 2, 1, 3, 1, 2, 1, 3, 2, 3, 1, 3, 2, 3, 1, 2, 1, 3, 1, 2, 3, 2, 1, 3, 1, 2, 1, 3, 2, 3, 1, 3, 2, 1, 2, 3, 2, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

A concatenation of blocks u_k, k >= 0, where u_k has length 5^k. The sequence is defined recursively - see the Maple code.

REFERENCES

B. Bollobas, The Art of Mathematics: Coffee Time in Memphis, Cambridge, 2006, p. 226.

LINKS

Table of n, a(n) for n=0..104.

MAPLE

a:=[1, 2, 3, 2, 1]; b:=[2, 3, 1, 3, 2]; c:=[3, 1, 2, 1, 3]; S:=[1];

for m from 1 to 6 do S:=subs({1=a[], 2=b[], 3=c[]}, S); od: S;

CROSSREFS

Cf. A010060, A005678-A005681, A006156, A007413.

Sequence in context: A260342 A281939 A002175 * A068073 A032452 A084199

Adjacent sequences:  A170820 A170821 A170822 * A170824 A170825 A170826

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 25 2009

STATUS

approved

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Last modified February 19 22:38 EST 2019. Contains 320328 sequences. (Running on oeis4.)