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Subsequence of Thue-Morse sequence
Problem 361
Published on 04 December 2011 at 04:00 am [Server Time]
The Thue-Morse sequence {Tn} is a binary sequence satisfying:
- T0 = 0
- T2n = Tn
- T2n+1 = 1 - Tn
The first several terms of {Tn} are given as follows:
01101001100101101001011001101001....
We define {An} as the sorted sequence of integers such that the binary expression of each element appears as a subsequence in {Tn}.
For example, the decimal number 18 is expressed as 10010 in binary. 10010 appears in {Tn} (T8 to T12), so 18 is an element of {An}.
The decimal number 14 is expressed as 1110 in binary. 1110 never appears in {Tn}, so 14 is not an element of {An}.
The first several terms of An are given as follows:
n | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | … |
An | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 9 | 10 | 11 | 12 | 13 | 18 | … |
We can also verify that A100 = 3251 and A1000 = 80852364498.
Find the last 9 digits of .
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