The prime factors of 91 are 13, 7, 1, 1, 7 and 13.
http://www.chacha.com/question/whatistheprimef...

Their greatest common factor is 13. Because 78=3X2X13. 91=13X7. Source(s) Me.
http://answers.yahoo.com/question/index?qid=200703...

Coco
http://www.blurtit.com/q3631379.html
