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Let . We study sufficient/necessary conditions, in terms of the coefficients An, for a function f ∈ A to be member of well-known subclasses of the class S of univalent functions. Examples of these subclasses include starlike, convex, close-to-convex functions. In particular, functions of the form z₂F₁ (a, b; c; z) are considered, where ₂F₁(a, b; c; z) is the hypergeometric function.