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Recurrence relations of perturbation theory for hydrogen ground state areobtained. With their aid polarizabilities in constant perpendicular electricand magnetic fields are computed up to 80th order. The high orders asymptoticis compared with its quasiclassical estimate. For the case of arbitrary mutualorientation of external fields a general sixth order formula is given.Comment: 11 pages, LaTeX, 2 figures (eps

Investigating the hydrogen atom in crossed external fields by the method of moments