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PROJECT EULER · #0739

Summation of Summations

Statement only · SolvedOriginal problem ↗

Take a sequence of length n. Discard the first term then make a sequence of the partial summations. Continue to do this over and over until we are left with a single term. We define this to be f(n).

Consider the example where we start with a sequence of length 8:

11111111123456725914202751428487514429016542132297132429429

Then the final number is 429, so f(8)=429.

For this problem we start with the sequence 1,3,4,7,11,18,29,47,
This is the Lucas sequence where two terms are added to get the next term.
Applying the same process as above we get f(8)=2663.
You are also given f(20)=742296999 modulo 1000000007

Find f(108). Give your answer modulo 1000000007.

Write-up coming later

The complete problem is available here. An approach, code, and answer will be added later.