Typeset the decimal representation of <number>, where <number> may be either an octal, decimal, or hexadecimal integer; or a register or parameter that contains an integer. Leading zeros are removed.
Recall that octals are represented by placing a ' (right quote) in front of the number, and hexadecimal are represented by placing a " (quotation mark) in front of the number, for example, '10 is the octal representation of 8, while "10 is the hexadecimal representation of 16. So
will typeset 8, while
will typeset 16.
The parameter \day contains the current day of the current month, unless it has been set otherwise. If today is, say, June 30th, then normally \day should contain 30, and
will typeset 30.
This functionality of \number overlaps with the command \the.