Abstract
This paper aims to establish conditions for the existence, uniqueness and Ulam-Hyers stability of solutions for a coupled system of pantograph problem with three sequential fractional derivatives. Two results on the uniqueness and existence of solutions are proved to utilize the Leray-Schauder and Banach fixed point theorems and positive contraction-type inequalities. Also, the stability in the sense of Ulam-Hyers and Ulam-Hyers-Rassias are studied. An illustrative example with graphical and numerical simulations is also proposed.