The following theorem, originally imparted to me by an algebra professor in the UCLA math department (grad school), may be helpful to you when testing yourself:

The following theorem, originally imparted to me by an algebra professor in the UCLA math department (grad school), may be helpful to you when testing yourself: Theorem. All numbers < 100 that look prime, are prime EXCEPT 91. (My addendum) Where "look prime" means, is not a multiple of 2, 3, 5, 11, nor a perfect square. All these numbers have quick tests for divisibility. Note that 91 = 7 * 13.