On the Eigenvalues of Certain Canonical Higher-Order Ordinary   Differential Operators
  We consider the operator of taking the $2p$th derivative of a function with zero boundary conditions for the function and its first $p-1$ derivatives at two distinct points. Our main result provides an asymptotic formula for the eigenvalues and resolves a question on the appearance of certain regular numbers in the eigenvalue sequences for $p=1$ and $p=3$. 
Albrecht Boettcher and Harold Widom