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# The atomic numbers of elements of the lanthanide series lie in the range of

$\begin{array}{1 1}\text{58 to 71}\\\text{57 to 70}\\\text{59 to 72}\\\text{56 to 69}\end{array}$

In lanthanides,4f orbitals are filled.Prior to this,$6s^2$ and $5d^1$ are filled.The sixth period starts from atomic number 55(=2+8+8+18+18+1).Hence,lanthanide starts from atomic number 58 and go up to atomic number 71.