Quote:
Originally Posted by andi314
so which other methods could i use to determine that a number is 100% prime???

For numbers having no special form, there are a number of algorithms you could try, e.g. APRCL (named after its inventors), ECPP, or the recent deterministic AKS algorithm. Do a Google search on any of these and you'll find background info and in most case freeware implementations. The practical limit of these seems to be 500010000 digits at present  proving any number < 100 digits or so would be virtually instantaneous via these methods.