Fifteen spread out to flank hundred and one? Well-organised (9)

I believe the answer is:

efficient

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'well-organised' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for efficient that I've seen before include "Performing with little wastage" , "Capable" , "Producing results with little waste of effort" , "Working well with little waste" , "Businesslike" .)

I've seen this clue in The Hindu.

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