Math Is Fun Forum

cheer99

Member

Registered: 2005-05-19

Posts: 8

Re: Puzzling Puzzle

Ellie-We had that in our math class as well...thank you very much!

cheer99

Member

Registered: 2005-05-19

Posts: 8

Re: Puzzling Puzzle

lol! More like your trying to get the ansewer for this weeks Lenny Conundrem on neopets.com!

I'm much rather have the extra 10 points on the exam, then try and win pretty much nothing on neopets.com. Can't help it if my math teacher used that question as well.

Anywho...just so the admin who helped with the question knows..the answer is 0.

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Puzzling Puzzle

"what is the number of prime numbers between one and a million that become a perfect square if you add 1 to them?"

Surely the number 3 qualifies ... add 1 you get 4 which is 2*2

So the answer is 1, isn't it?

---

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

jaz

Guest

Re: Puzzling Puzzle

just came here while googling...
so, a formal proof:
p be such a prime number,
=> p+1 = n^2, where n is natural =>
=> p = n^2 - 1
=> p = (n-1)(n+1), but hey, p is prime!
=> that can only be if n-1 = 1, that is p = 3
=> only one such prime number

MathsIsFun

Administrator

Registered: 2005-01-21

Posts: 7,713

Re: Puzzling Puzzle

Way cool, jaz. Neat and simple.

Ummm ... don't just drop a pearl of wisdom in passing ... join up and give us a few (not TOO hard) puzzles, or help out at the "Help Me" forum. (Though things may be quietening down here soon, as Summer Holidays are nearly upon us!)

---

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman