Similarities between chemistry of lanthanoids and actinoids are as follows:
Both, lanthanides and actinides show +3 oxidation state.
In both the series, the f-orbitals are filled gradually.
Ionic radius of the elements in both the series decreases with increase in atomic number.
Electronegativity in both the series is low for all the elements.
They all are highly reactive.
The nitrates, perchlorates and sulphates of all elements are soluble while their hydroxides, theorides and carbonates are insoluble.
Final answer:
The lanthanides actinides both are in the same category of inner transition metals and they both have 14 elements.