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PROJECT EULER · #0361

Subsequence of Thue-Morse Sequence

Statement only · UnsolvedOriginal problem ↗

The Thue-Morse sequence {Tn} is a binary sequence satisfying:

  • T0=0
  • T2n=Tn
  • T2n+1=1Tn

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 k=118A10k.

Write-up coming later

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