The relation a R b  defined by a is factor ofb on N is not

For a ∈ N, a is a factor of a so R is reflexive.If a is factor b and b is factor of c then a is factor of c   so R istransitive. If a is factor of b and b is factor of a then a = b soR is anti symmetric, 2 is factor of 4 but 4 is not a factor of 2.