Running a threadless application on a Intel Core2 CPU

My processor:

cat /proc/cpuinfo

ventrix@bytemobile:~$ cat /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 15
model name : Intel(R) Core(TM)2 CPU 6300 @ 1.86GHz
stepping : 6
cpu MHz : 1875.766
cache size : 2048 KB
physical id : 0
siblings : 2
core id : 0
cpu cores : 2

I created an application to test if a number is prime or not. It isn't very special, except the fact that you can check REALLY big numbers...

The result is this:


As you can see with htop, only one of the cores is executing the application.
Also, if you take a careful look at the xfce's cpu meter, the total use of the CPU counts a 50% percent.

After 25 minutes I guess 170141183460469231731687303715884105727 IS a big number to test:)
[BTW 170141183460469231731687303715884105727 is a prime, according to http://en.wikipedia.org/wiki/List_of_prime_numbers)