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PROJECT EULER · #0319

Bounded Sequences

Statement only · SolvedOriginal problem ↗

Let x1,x2,,xn be a sequence of length n such that:

  • x1=2
  • for all 1<in: xi1<xi
  • for all i and j with 1i,jn: (xi)j<(xj+1)i.

There are only five such sequences of length 2, namely: {2,4}, {2,5}, {2,6}, {2,7} and {2,8}.
There are 293 such sequences of length 5; three examples are given below:
{2,5,11,25,55}, {2,6,14,36,88}, {2,8,22,64,181}.

Let t(n) denote the number of such sequences of length n.
You are given that t(10)=86195 and t(20)=5227991891.

Find t(1010) and give your answer modulo 109.

Write-up coming later

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