In this paper we give various finiteness results concerning terms of recurrence sequences
U-n representable as a sum of S-units with a fixed number of terms. We prove that
under certain (necessary) conditions, the number of indices n for which U-n allows
such a representation is finite, and can be bounded in terms of the parameters involved.
In this generality, our result is ineffective, i.e. we cannot bound the size of the
exceptional indices. We also give an effective result, under some stronger assumptions.
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