\(D=8+8^3+8^5+...+8^{2x+1}\)
\(\Rightarrow64D=8^3+8^5+...+8^{2x+3}\)
\(\Rightarrow63D=64D-D=8^3+8^5+...+8^{2x+3}-8-8^3-...-8^{2x+1}=8^{2x+3}-8\)
\(\Rightarrow8^{2x+3}-8+8=8^{51}\)
\(\Rightarrow8^{2x+3}=8^{51}\Rightarrow2x+3=51\Rightarrow2x=48\Rightarrow x=24\)


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