Explanation
In the vi editor, one of the ways to issue commands multiple times or apply them to multiple rows is to specify the number right in front of a command. This will repeat the command as many times as the number indicates.
For example, the command 4l will move the cursor four characters to the right, and the command 2yj will copy two lines from the current line to the buffer. This method can be used for most of the vi commands that operate on single characters, words, lines, or blocks of text. Another way to issue commands multiple times or apply them to multiple rows is to use the . (dot) command, which repeats the last command. For example, after deleting a line with dd, pressing . will delete another line. However, this method is less precise and efficient than specifying the number before the command. References:
* Basic vi commands (cheat sheet), Topic: Moving within a File (Navigation).
* Vi Editor with Commands in Linux/Unix Tutorial, Topic: VI Editing commands.