Singular numbers and Stickelberger relation
  Let p be an odd prime. Let K_p = Q(zeta) be the p-cyclotomic field. Let pi be the prime ideal of K_p lying over p. Let G be the Galois group of K_p. Let v be a primitive root mod p. Let sigma be a Q-isomorphism of K_p. Let P(sigma) = sigma^{p-2}v^{-(p-2)}+ ... + sigma v^{-1} +1 in Z[G], where v^n is understood (mod p). We apply Stickelberger relation to odd prime numbers q different of p and to some singular integers A of K_p connected with the p-class group C_p of K_p and prove the pi-adic congruences:   1) pi^{2p-1} | A^{P(\sigma)} if q = 1 (mod p),   2) pi^{2p-1} || A^{P(\sigma)} if q = 1 (mod p) and p^{(q-1)/p} = 1 (mod q).   3) pi^{2p} | A^{P(\sigma)} if q not = 1 (mod p).   These results allow us to connect the structure of the p-class group C_p with pi-adic expression of singular numbers A and with solutions of some explicit congruences mod p in Z[X].   The last secion applies Stickelberger relation to describe the structure of the complete class group of K_p. 
Roland Queme