Find all triples of positive integers (x,y,z) such that Find all triples of positive integers (x,y,z) such that
$x^{z+1} \ - \ y^{z+1}=2^{100}$
The RHS is even, then x and y must be odd and $x^{z+1}>y^{z+1}$, but how to find out them all ?
 A: You can factor $x^{z+1}-y^{z+1}$ by dividing out $x-y$.  This shows that $x-y$ is a power of $2.$  But they must only have the same parity-they can both be even.  In particular, there are many solutions with $z=0$  If $z=1$ you can factor it as $(x-y)(x+y)=2^{100}$ and you can find a finite number of solutions here.  I think, but have not proved, that you will not find any with larger $z$.
A: $x \ge 0 \land y \ge 0 \rightarrow x \ge y$.
$$x^{z+1} - y^{z+1} = \left(x - y\right)\left(x^z + x^{z-1}y + x^{z-2}y^2 + \dots  +y^z\right) = 2^{k+1} \tag{T1}$$
So we can conclude $x - y = 2^{r_1}$, and that $x$ and $y$ have the same parity.

If $z$ is even, rewrite $(T1)$:
$$x^z + y^z + xy\underbrace{\left(x^{z-2} + x^{z-3}y + \dots  + y^{z-2}\right)}_{\text{An odd number of terms}} = 2^{k} \tag{T2}$$
Since $x$ and $y$ have the same parity then $x$ and $y$ must both be even to satisfy the parity of $(T2)$.  Let $2a = x$ and $2b = y$.
$$a^{z+1} - b^{z+1} = 2^{k - z}$$
which is a smaller instance of the original problem with the added assumption that $z$ is even.  We can repeat the proof to get either $\exists c\, d\, : 2c = a \land 2d = b$ or that $2^{k - \dots}$ is no longer an integer, ad nauseam.

If $z$ is odd,
$$x^{z+1} - y^{z+1} = \left(x + y\right)\left(x^z - x^{z-1}y + x^{z-2}y^2 - \dots  -y^z\right) = 2^{k}$$
Conclude odd $z$ leaves a system of equations
  $$x-y = 2^{r_1}$$
  $$x+y = 2^{r_2}$$
$x = 2^{r_2 -1} + 2^{r_1 - 1}, y = 2^{r_2 -1} - 2^{r_1 - 1}$
Expanding $x^{z+1} - y^{z+1} = 2^{k+1}$ for $z=1$ gives a set of solutions:
$$2^{r_1 + r_2} = 2^{k+1}$$
$$(x,y,z) \in (2^{n - 1} + 2^{k - n},2^{n - 1} - 2^{k - n},1)\, 1 \le n \le k$$
Expanding for $z = 3$ gives another set:
$$2^{3r_2 + r_1 - 1} + 2^{3r_1 + r_2 - 1} = 2^{k+1}$$
with $(x,y,z)$ being found by the $r_1$ and $r_2$ values that satisfy the above.
At this point I'm unsure how to continue.   All further expansions $z > 3$ seem to involve only positive terms, some of the form $A\cdot 2^{B(r_1, r_2)}\, ,\, A \ne 2$, which comes from the binomial expansion.  It might be provable by induction.  If so, then there are no more solutions.
