Is 91 prime?

I was surfing around online and came across this very interesting article about seeing if a number is prime. We can all check to see if it's divisible by 2 or 5 and usually 3, but this gives useful hints to see if a number is divisible by 7 or 11, too. Very interesting read.

http://balltech.blogspot.com/2008/03/is-91-prime.html