Register to reply

An algebra prove question

by numberthree
Tags: algebra, prove
Share this thread:
Mar9-11, 06:54 PM
P: 8
1. The problem statement, all variables and given/known data

Prove that if one of the numbers 2n-1 and 2n+1 is prime, n>2, then the other number is not

2. Relevant equations

3. The attempt at a solution
Phys.Org News Partner Science news on
Hoverbike drone project for air transport takes off
Earlier Stone Age artifacts found in Northern Cape of South Africa
Study reveals new characteristics of complex oxide surfaces
Char. Limit
Mar9-11, 07:25 PM
PF Gold
Char. Limit's Avatar
P: 1,941
What have you tried?
Mar9-11, 07:27 PM
P: 8
I dont even know how to start.

Mar9-11, 08:35 PM
P: 21,216
An algebra prove question

Part 1: Pick one of the numbers, and assume it is a prime larger than 2. Then show that the other number is not prime.

Part 2: Now pick the other number, and assume it is a prime larger than 2. Then show that the other number is not prime.
Mar19-11, 11:32 PM
P: 44
I dont the result is correct but.....2^n-1 is prime when n is an odd number.....not all odd number but n has to be of the odd form.......and 2^n+1 is prime.....when n is some even number.....

can somebody tell me if it is correct......
Mar20-11, 12:41 AM
P: 7
Have you thought about using mathematical induction?

Set up your base case: n = 3
You will show that [tex]2^3-1 = 8 - 1 = 7[/tex] is prime and [tex]2^3 + 1 = 9 [/tex] is not since [tex] 9 = 3 \cdot 3[/tex].

Assume that it's true for n. Then prove the case for n + 1.

Register to reply

Related Discussions
Operation algebra: prove [A,f(A)]=0 Introductory Physics Homework 1
Linear Algebra - Prove that E is not a basis for V. Calculus & Beyond Homework 9
Algebra prove Precalculus Mathematics Homework 2
Abstract Algebra: Prove Unit question Calculus & Beyond Homework 2
How do I prove this? [Linear Algebra] Introductory Physics Homework 3