The main result of this paper is that if a sequence of complex numbers (a(n
))(n greater than or equal to 0) satisfies
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for some integer r greater than or equal to 0, then a(n) = 0 for all n > r.
As an application, we deduce a localized form of a theorem of Allan about
nilpotent elements in Banach algebras, and this in turn leads to an invaria
nt-subspace theorem. As a further application, we prove a Variant of Carlem
an's theorem on the unique determination of probability distributions by th
eir moments. The paper concludes with a quantitative form of the main resul
t.