The above question can be answered on the basis of reasoning from analogy. We note that two periods have to pass before d-orbitals begin to fill. This is also true of the spot where f-orbitals commence filling. The second row where f-orbitals fill happens to be row #7 (the one starting with Fr). The first element where 5f-orbitals enter in is actinium (Ac, Z = 89). Adding 32 to this would give element #121 termed as Unbiunium, the first Super-Actinide.