“…For example, they play a role in complex analysis, number theory, potential theory, probability theory [9], physics [20], numerical and asymptotic analysis, integral transforms [41], and combinatorics. Some related references are listed in [2,3,4,5,6,15,23,41]. In recent years, inequalities and (logarithmically) completely monotonic functions involving the gamma, psi, or polygamma functions are established by some mathematicians (see [2,3,4,11,15,17,21,31] and related references therein).…”