In perl, numbers are double-precision floating point, unless you use integer;. Doubles have 52 bits of mantissa in many architectures, so they can represent integers that are quite a bit larger than 32-bit ints. They'll eventually run out of room and start rounding off, though.

You can use larger integers by using Math::BigInt or the like, but I doubt you'll be able to get a module like Set::IntSpan to use bigints.