Question 754933
How advanced is your course or class?  The best is to know the common rules about factoring.  Knowing if a number is prime or  not is tricky after the first hundred natural numbers.  If the 6digit number is odd, look in a table of prime numbers.  If it's not there, then some factorization will be possible.


Remember the rules for 2, 3, 5, 9, 10.  After those, start checking about prime factors.