Math Is Fun Forum

a sequence of natural numbers χ1,χ2,...,χn called:
1) "supertwofold" if for every term of her except the first forces xn+1 > 2xn.
2) "twofold" if for every terms of her except the first forces xn+1=2xn.
3)"half" if for every term of her except the first forces xn+1 < 2xn.
And the question is....are the above sequences numerables?

I have no idea who i'll prove it...so if someone knows please help me.

thanks!!!

Hello, does anybody knows how to solve this problem:
Given the polynomials A=x^3 +2x -1 and B=x^2-x+3
evaluate them for  x= -2,-1,0,1,2,3 and calculate their product and its coefficients. And its interposition
I need another way on doing this, instead of calculating A and B one by one
(I shouldn't use the simple method ie.  ....).
How can this be done? Thank you.