Mass spectrum of heavy quarkonium for screened Kratzer potential (SKP) using series expansion methodE. E. Ibekwe, U. S. Okorie, J. B. Emah, E. P. Inyang and S. A. EkongEur. Phys. J. Plus, 136 1 (2021) 87DOI: https://doi.org/10.1140/epjp/s13360-021-01090-y