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We derive two equivalent analytical expressions for an lth partial-wave scattering length al for central potentials with long-range tails of the form V (r) = − ℏ 2 2 m B r n − 4 (r n − 2 + R n − 2) 2 − ℏ 2 2 m C r 2 (r n − 2 + R n − 2) , (r ⩾ rs, R > 0). For C = 0, this family of potentials reduces to the Lenz potentials discussed in a similar context in our earlier works [R. Szmytkowski, Acta Phys. Pol. A 79, 613 (1991); J. Phys. A: Math. Gen. 28, 7333 (1995)]. The formulas for al that we provide in this paper depend on the parameters B, C, and R characterizing the tail of the potential, on the core radius rs, as well as on the short-range scattering length als, the latter being due to the core part of the potential. The procedure, which may be viewed as an analytical extrapolation from als to al, is relied on the fact that the general solution to the zero-energy radial Schrödinger equation with the potential given above may be expressed analytically in terms of the generalized associated Legendre functions. [ABSTRACT FROM AUTHOR]