“…To our knowledge, there are only a few procedures for computing the coefficients E i (ω, n). They involve, in particular, applying the methods of the comparison equation [21] and complex "sprout" [22]; an analytic continuation in the h -plane [23]; various approaches within the framework of the WKB approximation [15][16][17][18][19]; quantization using the methods of classical mechanics [17,24]; and, lastly, expansions in the h1/2 -series [25]. However, all of these methods have some disadvantages.…”