The value of $B = 1001$
And we can see that $C = 2B + 1 \Rightarrow 2B + (2-1)$
$D=2C+1=4B+3 \Rightarrow 2^2B+(2^2-1)$
$E =2D+1=8B+7 \Rightarrow 2^3B+(2^3-1)$
$\vdots$
$\vdots$
$Z=2Y+1 \Rightarrow 2^{24}B+(2^{24}-1)$
Now $\frac{Z+1}{2^{25}} = \frac{2^{24}(B+1)-1]+1)}{2^{25}} = \frac{B+1}{2}=501$