Let C-A((n))(D) denote the algebra of all n-times continuously differentiable functions on (D) over bar which are holomorphic on the unit disc D = {z is an element of C: \z\< 1}. We prove that C-A((n))(D) is a Banach algebra with multiplication as Duhamel product (f*g)(z) = d/dz integral(z)(o) f(z - )g(t)dt and describe its maximal ideal space. We also describe the commutant and strong cyclic vectors of the integration operator (Tf)(z) = integral(z)(o)f(t)dt. Using the Duhamel product we also study the extended eigenvalues and the corresponding extended eigenvectors of the integration operator T.