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 A324474 Nonzero ternary words such that any non-initial 1 is preceded by 0, and any non-initial 2 is preceded by 00. 2

%I

%S 1,2,10,20,100,101,200,201,1000,1001,1002,1010,2000,2001,2002,2010,

%T 10000,10001,10002,10010,10020,10100,10101,20000,20001,20002,20010,

%U 20020,20100,20101,100000,100001,100002,100010,100020,100100,100101,100200,100201

%N Nonzero ternary words such that any non-initial 1 is preceded by 0, and any non-initial 2 is preceded by 00.

%C This could have begun with an initial 0, but (since this is a list, and must have offset 1), we would no longer have a(1)=1, and that is needed for some related sequences.

%C The indices of words of the form 100...00 are 1, 3, 5, 9, 17, 31, ..., see the tribonacci numbers A000213.

%H N. J. A. Sloane, <a href="/A324474/b324474.txt">Table of n, a(n) for n = 1..845</a>

%e The initial terms, as a list:

%e 1

%e 2

%e 10

%e 20

%e 100

%e 101

%e 200

%e 201

%e 1000

%e 1001

%e 1002

%e 1010

%e 2000

%e 2001

%e 2002

%e 2010

%e 10000

%e ...

%Y Cf. A007089, A324475, A000213.

%K nonn,base

%O 1,2

%A _Nathan Fox_ and _N. J. A. Sloane_, Mar 09 2019

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Last modified September 26 09:15 EDT 2021. Contains 347664 sequences. (Running on oeis4.)