Square of an octal number

Question

How to find the square of an octal number.

For example what will be the square of $23$.

It will not be $529$ because octal number system does not have digit $7$.

Answer 1

\begin{align}23^2&=(20+3)^2\\&=20^2+2\times20\times3+3^2\\&=400+140+11\\&=551.\end{align}