34L10 Eigenfunctions, eigenfunction expansions, completeness of eigenfunctions of ordinary differential operators 1576

34L15 Eigenvalues, estimation of eigenvalues, upper and lower bounds of ordinary differential operators 1890

34L16 Numerical approximation of eigenvalues and of other parts of the spectrum of ordinary differential operators 521

34L20 Asymptotic distribution of eigenvalues, asymptotic theory of eigenfunctions for ordinary differential operators 1098