The largest integer R can hold is
.Machine$integer.max #  2147483647
This has nothing to do with scientific notation and everything to do with how the computer actually stores the numbers. The current version of R stores integers still as 32bit, regardless of the architecture. This might change in the future though.
Currently you can get access to 64 bit integers through the int64 package
> as.integer(.Machine$integer.max)  2147483647 > # We get problems with this > as.integer(.Machine$integer.max + 1)  NA Warning message: NAs introduced by coercion > # But if we use int64 > library(int64) > as.int64(.Machine$integer.max) + 1L  2147483648