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We combine measurements of the top quark pair production cross section in pp collisions in the ℓ + jets, ℓℓ, and τℓ final states (where ℓ is an electron or muon) at a center of mass energy of √s = 1.96 TeV in 1 fb-1 of data collected with the D0 detector. For a top quark mass of 170 GeV/c2, we obtain σtt = 8.18-0.87+0.98 pb in agreement with the theoretical prediction. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined tt cross section, consistent with the world average of the top quark mass. In addition, the ratios of tt cross sections in different final states are used to set upper limits on the branching fractions B(t → H+b → τ+vb) and B(t → H+b → csb) as a function of the charged Higgs boson mass.