In the article A Four Dimensional Generalization of the Quantum Hall Effect, arXiv:cond-mat/0110572, by Zhang and Hu Quadratic Casimir operator for $SO(5)$ is given as
$$p^2/2+q^2/2+2p+q .$$
When $SO(5)$ irreducible representations are labelled by $(p,q)$
But In Iachello's book Lie algebras and Applications, it is given as
$$2p^2+6p+2q^2+2q.$$
Why are those two different?