Change to firstprivate instead of private.
Add clean target to Makefile.
Run `make clean` to delete files produced by make. Will be more useful when you have multiple targets making object files.
Merge branch 'master' of https://github.com/ofb/c

Conflicts:
	char.c++
Merge branch 'master' of https://github.com/ofb/c
Merge branch 'master' of https://github.com/ofb/c
Add check for valid primes.
Ensure that the input for the program doesn't create primes greater than 60 000, which would overflow the unsigned long long data type.
Merge pull request #6 from geppettodivacin/master

Add check for valid primes.