Which Urbanik class $L_k$, do the hyperbolic and the generalized logistic characteristic functions belong to?

Abstract

Selfdecomposable variables obtained from series of Laplace (double exponential) variables are objects of this study. We proved that hyperbolic-sine and hyperbolic-cosine variables are in the difference of the Urbanik classes $L_2$ and $L_3$ while generalized logistic variable is at least in the Urbanik class $L_1$. Hence some ratios of those corresponding selfdecomposable characteristic functions are again selfdecomposable.