Abstract
We investigate a general sequential hybrid class of fractional differential equations in the Caputo and Atangana-Baleanu fractional senses of derivatives. We consider the existence and uniqueness of solutions and the Hyers-Ulam (H-U) stability for a general class. We use the Banach and Leray-Schauder alternative theorems for the existence criteria. With the help of nonnegative Green's functions, the fractional-order class is turned into m-equivalent integral forms. As an application of our problem, a fractional-order smoking model in terms of the Atangana-Baleanu derivative is presented as a particular case.