<P> Equivalently, an ideal of R is a sub-R - bimodule of R . </P> <P> A subset I (\ displaystyle I) of R (\ displaystyle R) is called a right ideal of R (\ displaystyle R) if it is an additive subgroup of R and absorbs multiplication on the right, that is: </P> <Ol> <Li> (I, +) (\ displaystyle (I, +)) is a subgroup of (R, +) (\ displaystyle (R, +)) </Li> <Li> ∀ x ∈ I, ∀ r ∈ R: x ⋅ r ∈ I . (\ displaystyle \ forall x \ in I, \ forall r \ in R: \ quad x \ cdot r \ in I .) </Li> </Ol> <Li> (I, +) (\ displaystyle (I, +)) is a subgroup of (R, +) (\ displaystyle (R, +)) </Li>

The number of proper ideal of z17 is