Perturbation theory for sextic doubly anharmonic oscillator
  A simple method for the calculation of higher orders of the logarithmic perturbation theory for bound states of the spherical anharmonic oscillator is developed. The structure of the perturbation series for energy eigenvalues of the sextic doubly anharmonic oscillator is investigated. The recursion technique for deriving renormalized perturbation expansions is offered. 
I. V. Dobrovolska, R. S. Tutik