Fermat numbers

[Lottasv]

Please help me with this (see photo) I got a tip and It said that a Fermat number is always odd so if a number b exists such that b^3=Fe_n then we have b like b=(2k+1)
And then develop b^3 , but how do I do it?

 

[Deleted member 4993]

Please help me with this (see photo) I got a tip and It said that a Fermat number is always odd so if a number b exists such that b^3=Fe_n then we have b like b=(2k+1)
And then develop b^3 , but how do I do it?

(x + y )^3 = x^3 + 3*x^2*y + 3*x*y^2 + y^3

 

[Lottasv]

But how do I do that on my question?

 

[Deleted member 4993]

But how do I do that on my question?

b^3 = (2k +1)^3 = ???

However, Fermat numbers are of the form:

b =

 

[Lottasv]

Thank you but I don’t understand what that equals?

 

[Deleted member 4993]

Thank you but I don’t understand what that equals?

There are two definitions of Fermat numbers - which definition are you following?