15-7-2009 : arithmetic progressions

1) Prove that there exist arbitrarily long arithmetic progressions with all the terms being powers of integers.

5 Answers

39
Dr.House ·

no single taker?

9
Celestine preetham ·

ofc dude its obvious

eg 1 1 1 1 1 1

4 4 4 4 4 4 4 4 4 4 ..........

62
Lokesh Verma ·

even i was going to give the same solution :D

but then i thought that it wud be unfair to the question ;)

I am sure the question has the phrase "unequal terms"

I have seen the question but dont know the prooff.. the proof i saw had arguments on Real analysis!

9
Celestine preetham ·

i guess proof gots to deal with the fact we got infinite no of powers of integers

39
Dr.House ·

By rk denote member of the finite arithmetic progression

n!+1+k(n-1)!,k=1..n.

It is obvious gcd(ri,rj)=1.

Let ai=si*r1*r2*...*rn/ri,
si is positive integer and satisfies the condition

ri|(ai+1) (gcd(r1*r2*...*rn/ri ,ri)=1

==>si exists.

Denote m=r1a1*...*rnan.

The sequence r1*m, r2*m,..., rn*m is required since rk*m=b^rk for some positive integer b.

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