  We define a group stucture on the primitive integer points (A,B,C) of the
algebraic variety Q_0(B,C)=A^n, where Q_0 is the principal binary quadratic
form of fundamental discriminant \Delta and n is a fixed integer greater than
1. A surjective homomorphism is given from this group to the $n$-torsion
subgroup of the narrow ideal class group of the quadratic number field
Q(\sqrt{\Delta}).
