You can refer thisto the literals_rdocliterals documentation to knowfind the special prefixprefixs to write numbers in decimal, hexadecimal, octal or binary formats.
For decimal numbers use a prefix of 0d, for hexadecimal numbers use a prefix of 0x, for octal numbers use a prefix of 0 or 0o, for binary numbers use a prefix of 0b. The alphabetic component of the number is not case-sensitive.
21 or 0d21 is considered as number in decimal format but 021 is considered as number in octal format. And when interpreted to print it, it uses default decimal format.