A Closed-Form Solution to the Arbitrary Order Cauchy Problem with   Propagators
  The general abstract arbitrary order (N) Cauchy problem was solved in a closed form as a sum of exponential propagator functions. The infinite sparse exponential series was solved with the aid of a homogeneous differential equation. It generated a linear combination of exponential functions. The Cauchy problem solution was formed with N linear combinations of N exponential propagators. 
Henrik Stenlund
math.GM