Regarding the van der Waals constant which of the following is/are correct ?

In van der Waals equation $\left(\mathrm{P}+\frac{{\mathrm{an}}^2}{{\mathrm{V}}^2}\right)\left(\mathrm{V}-\mathrm{nb}\right)=\mathrm{nRT}$

“a” & “b” are the characteristic constants not the universal gas constant and depends on the intramolecular interactions and size of the gas molecule respectively