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PROJECT EULER · #0617

Mirror Power Sequence

Statement only · UnsolvedOriginal problem ↗

For two integers n,e>1, we define an (n,e)-MPS (Mirror Power Sequence) to be an infinite sequence of integers (ai)i0 such that for all i0, ai+1=min(aie,naie) and ai>1.
Examples of such sequences are the two (18,2)-MPS sequences made of alternating 2 and 4.

Note that even though such a sequence is uniquely determined by n,e and a0, for most values such a sequence does not exist. For example, no (n,e)-MPS exists for n<6.

Define C(n) to be the number of (n,e)-MPS for some e, and D(N)=n=2NC(n).
You are given that D(10)=2, D(100)=21, D(1000)=69, D(106)=1303 and D(1012)=1014800.

Find D(1018).

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