GNU Emacs Lisp Reference Manual

2.3.1: Integer Type

The range of values for integers in Emacs Lisp is -134217728 to 134217727 (28 bits; i.e., -2**27 to 2**27 - 1) on most machines. (Some machines may provide a wider range.) It is important to note that the Emacs Lisp arithmetic functions do not check for overflow. Thus (1+ 134217727) is -134217728 on most machines.

The read syntax for integers is a sequence of (base ten) digits with an optional sign at the beginning and an optional period at the end. The printed representation produced by the Lisp interpreter never has a leading `+' or a final `.'.

-1               ; The integer -1.
1                ; The integer 1.
1.               ; Also The integer 1.
+1               ; Also the integer 1.
268435457        ; Also the integer 1! 
                 ;   (on a 28-bit implementation)

See Numbers, for more information.