Gaussian 03 Online Manual
The route section of a Gaussian job is initiated by a pound sign (#) as the first non-blank character of a line. The remainder of the section is in free-field format. For most jobs, all of the information can be placed on this first line, but overflow to other lines (which may but need not begin with a # symbol) is permissible. The route section must be terminated by a blank line.
If no keywords are present in the route section, the calculation defaults to HF/STO-3G SP.