Looking at the version history it isn't clear when the feature was
added, but in 7.1.1 there was a bug fixed that seems relevant:
http://www.cs.wisc.edu/condor/manual/v7.1/8_Version_History.html
http://www.cs.wisc.edu/condor/manual/v7.1/8_3Development_Release.html#SECTION00933000000000000000
Condor now coerces the result of $$([]) expressions within submit
description files to strings. This means that submit files can do simple
arithmetic. For example, you can describe a command-line argument as:
arguments = $$([$(PROCESS)+100])
and condor_ submit will expand the argument to be the expected value.