What is the greatest prime factor of 2^10 - 1?	Choose the correct option.
A) 17  B) 19  C) 23  D) 29  E) 31
2^10-1 = (2^5-1)(2^5+1) = 31*33   The answer is 31.
<result>E</result>
What is the greatest prime factor of 2^10 - 1?