From CS2800 wiki

The most common number base is base 10, or decimal. This is how we usually interpret numbers. It is convenient because most people have ten fingers and that's how we first learn to count.

No special notation is needed to indicate decimal, since that's how we normally interpret numbers. For example, [math]1234 [/math] means [math]\href{/cs2800/wiki/index.php/Base}{(1234)_{10}} [/math].