Max AutoCAD entity handle number

The handle value is stored as a 64 bit number (8 bytes) in the DWG file no matter if you run 32-bit or 64-bit AutoCAD. The maximum value for a handle is: "FFFFFFFFFFFFFFFF" as hexadecimal or 6744073709551615 as integer.

If you for example use the LIST command you see the handle listed:
Handle = 1e9

Or if you list the properties using AutoLISP:
(entget(car(entsel)))
that can give a result like this:
(5 . "1E9")

If you with AutoLISP want to delete an object based on its handle ("1E9") this can be used:
(entdel(handent "1e9"))

The last tip can be useful if you have a problem with for example:
*Warning* Multiply owned object, handle "1e9"