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

1, 2, 10, 20, 100, 101, 200, 201, 1000, 1001, 1002, 1010, 2000, 2001, 2002, 2010, 10000, 10001, 10002, 10010, 10020, 10100, 10101, 20000, 20001, 20002, 20010, 20020, 20100, 20101, 100000, 100001, 100002, 100010, 100020, 100100, 100101, 100200, 100201

Offset: 1

Author

Nathan Fox and N. J. A. Sloane, Mar 09 2019

Keywords

• nonn
• base

Comments

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.

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

Examples

			The initial terms, as a list:
1
2
10
20
100
101
200
201
1000
1001
1002
1010
2000
2001
2002
2010
10000
...
		

Links

• N. J. A. Sloane, Table of n, a(n) for n = 1..845

Crossrefs

Cf. A007089, A324475, A000213.