My first approach was to consider modulo 6.
Assume a > 6, Since a is prime we have a=1, -1 (mod 6)
Thus, a2=1 (mod 6).
We know, 26 = 2 (mod 6)
Therefore a2+26=3 (mod 6)
So any prime greater than 6 would be resulting in a number which is divisible by 3 which NOT prime as required.
So we have to check 2, 3 and 5 which are the only primes less than 6. It is easy to see that each would yield a non-prime in a2+26. So we're done!
Welcome to BrainDen.com - Brain Teasers Forum
|Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.
Of course, you can also enjoy our collection of amazing optical illusions and cool math games.
If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.
Thanks and enjoy the Den :-)
Guest Message by DevFuse
ABKMember Since 14 Sep 2012
Offline Last Active Sep 14 2012 03:16 PM
- Group Members
- Active Posts 1
- Profile Views 423
- Member Title Newbie
- Age Age Unknown
- Birthday Birthday Unknown