@j0eh4x:

# navigate to the crunch folder:
cd /pentest/passwords/crunch/

# execute crunch, generate a list with each password length of 10, using only numbers, first three are always '666'
./crunch 10 10 0123456789 -t 666@@@@@@@

I'm not on a linux box; so I can't test now. You should read the crunch help guide for more info:
./crunch --help