How Many Ordered Pairs (P, Q) Are There Such That The Unit's Digits Of P^P And Q^Q Are Same? Given That P And Q Are Natural Numbers Less Than 10?(a^b=a To The Power Of B)

The only natural numbers in the range 1-9 that have the same units digit when raised to their own power are
  4^4 = 256
  6^6 = 46,656
  8^8 = 16,777,216
From these 3 digits, 6 ordered pairs can be formed.
  (4, 6), (4, 8), (6, 8), (6, 4), (8, 4), (8, 6)
You can add 3 more pairs if P is allowed to be equal to Q.
  (4, 4), (6, 6), (8, 8)