Question

Let R₁ and R₂ be relations on the set {1, 2, ..., 50} such that R₁ = {(p, pⁿ) : p is a prime and n ≥ 0 is an integer} and R₂ = {(p, pⁿ) : p is a prime and n = 0 or 1}. Then, the number of elements in R₁ - R₂ is____.