##### 4.1.1.1 Integers

The constants include integers such as

```     0   1   999   -512
```

Besides the usual decimal, or base 10, notation, integers may also be written in other base notations. In `sicstus` mode, any base from 2 to 36 can be specified, while in `iso` mode bases 2 (binary), 8 (octal), and 16 (hex) can be used. Letters `A' through `Z' (upper or lower case) are used for bases greater than 10. E.g.:

```     15   2'1111   8'17  16'f  % sicstus mode
15   0b1111   0o17  0xf   % iso mode
```

all represent the integer fifteen. Except for the first, decimal, notation, the forms in the first line are only acceptable in `sicstus` mode, while those in the second line are only valid in `iso` mode.

There is also a special notation for character constants. E.g.:

```     0'A   0'\x41   0'\101
```

are all equivalent to `65` (the character code for `A'). `0'' followed by any character except `\' (backslash) is thus read as an integer. Unless character escapes have been switched off, if `0'' is followed by `\', the `\' denotes the start of an escape sequence with special meaning (see Escape Sequences).