A relation if reflexive iff ,
xRx exists . Which is true here since x= x^1 for all x $\in$ Z.Thus it is reflexive.
It is not symmetric , since (2,4) exists but (4,2) does not belong to the Relation .
It is anti-symmetric , because of the reflexive elements.
If xRy exists then y=x^i and if yRz exists then z=y^j . so we can write z = (x^i)^j.
Thus the relation is reflexive , anti-symmetric and transitive . Thus a Poset.