Sometimes we come up with fairly complex O() functions, but because the highest-order term will dominate the value as n increases, the convention is to remove all low-order terms, and not to bother showing any constant multiplying factors. O(n2/2+ 3n) is the same as O(n2/2), which is equivalent to O(n2). This is actually a weakness of the O() notation—one O(n2) algorithm may be 1,000 times faster than another O(n2) algorithm, but you won't know it from the notation.
