The octal number of 66789 is:
202345
The octal number system represents numbers in a system to the base of 8. It uses the digits 0 - 7.
Historically, the origins of octal number system is in the 17th Century.
The octal system of numbers is used in the computer science, because each digit of an octal number can be represented by three bits. For example, octal numbers are used in file access rights under the UNIX operating system.