--data
declare @t table (name int, OldFriendsName int)
insert @t
          select 1, null
union all select 2, 1
union all select 3, null
union all select 4, 1
union all select 5, 2
union all select 6, 3

--input
declare @name int
set @name = 1

--calculation
declare @OldFriends table (name int)
insert @OldFriends select @name

while @@rowcount > 0
begin
insert @OldFriends
    select b.name from @OldFriends a
        inner join @t b on a.name = b.OldFriendsName
    where b.name not in (select name from @OldFriends)
end

select * from @OldFriends where not name = @name order by name

/*results
name        
----------- 
2
4
5
*/