From local correlations to regional systematics
  Local correlations of $2^+_1$ excitation energies and B(E2, $2^+_1\rightarrow \text{ g.s.}$) values require linear $N_pN_n$ systematics in a logarithmic scale, as confirmed by an experiment survey. Based on local correlations of $\alpha$-decay energies, neutron separation energies, and proton separation energies, one can decouple them into their proton and neutron contributions separately. These contributions exhibit smooth regional systematics beyond the $N_pN_n$ scheme. 
Z. Z. Q, M. Bao and Y. Lei
nucl-th