List iteration removing n number of duplicates

So ive had a search and come to a standstill. I'm trying to iterate through a list and where entries appear n number of times remove those entries. the looping and clearing isn't a problem its the n entry. Im trying to use raw code rather than libraries. Any suggestions or pointers would be greatly appreciated! below is what i have been toying with. i have left it at the data.remove line as this is where i perceive i am lost!

n=2 
Data =({1, 2, 2, 3, 3, 3, 4, 5, 5}, 1)

def remove_dup(a):
    i = 0
    while i < len(a):
      j = i + 1

      while j < len(a):
         if a[i] == a[j]:

              Data.remove[j] where j==n
         else:
            j += 1
      i += 1


remove_dup(Data)

print(Data)