Question: odd has how many factors?
Answer: Number of odd factors will be all possible combinations of powers of 3 and 5 (excluding any power of 2) . Hence number of odd factors = (1+1)(1+1) = 4. By manually checking, these factors are 1, 3, 7 and 21. Number of even factors = total no. of factors - no. of even factors. = 12 - 4 = 8.