“HOMOTOPY PERTURBATION METHOD (HPM), ADOMIAN DECOMPOSITION METHOD (ADM) AND COUPLING HPM AND PEM (PARAMETER-EXPANSION METHOD) FOR NONLINEAR OSCILLATOR WITH COORDINATE-DEPENDENT MASS” (2025) Far East Journal of Mathematical Sciences (FJMS), 142(4), pp. 615–637. doi:10.17654/0972087125034.