A Formula For the S-Class Number of an Algebraic Torus
  We obtain a formula for the S-class number of an algebraic torus defined over a number field in terms of the etale and Galois cohomology groups of its character module. As applications, we give different proofs of some classical class number formulas of Shyr, Ono, Katayama and Morishita. 
Minh-Hoang Tran
math.NT