[1] Adachi N.: Generalization of Kummer's criterion for divisibility of class numbers. Jouгnal of Number Theoгy, 5 (1973), 253-265. MR 0332715 | Zbl 0263.12005

[2] Caгlitz L.: The first factor of the class number ofba cyclic field. Can. J. Math. vol. 6 (1953), 23-26.

[3] Narkiewicz W.: Elementary and analytic theory of algebraic numbers. Warszawa 1974. MR 0347767 | Zbl 0276.12002

[4] Pollaczek F.: Über die irregulären Kreiskörper der l-ten und $l^2$-ten Einheitswurzeln. Math. Z. 21 (1924), 1-38. MR 1544682

[5] Ribet K. A.: A modulas construction of unramified p-extensions of $Q(\mu_p)$. Inventiones mathematicae 34 (1976), 151-162. MR 0419403

[6] Vandiver H. S.: On the first factor of the class number of a cyciotomic field. Bull. Ameг. Math. Soc., 25 (1918-1919), 458-461. MR 1560224

[7] Wagstaff S. S., Jr.: The irregular primes to 125 000. Math. Comp., v. 32 (1978), 583-591 and the more detailed results: personal communication. MR 0491465