The big-O hierarchy: A few basic facts about the big-O behaviour of some familiar functions are very important. Let p(n) be a polynomial in n (of any degree). Then
logbn is O(p(n)) and p(n) is O(an);
for any base b and any a. In words: logs are big-O of polynomials and polynomials are big-O of exponentials.
Note that since logbn = logcn/ logcb, we have
logbn is O(logcn);
for any fixed b and c, since logcb is a constant.