\[\boxed{\mathbf{451}.}\]
\[1)\ \sqrt{\sqrt[3]{729}} = \sqrt[{2 \bullet 3}]{729} = \sqrt[6]{3^{6}} = 3;\]
\[2)\ \sqrt[5]{\sqrt{1024}} = \sqrt[{5 \bullet 2}]{1024} =\]
\[= \sqrt[10]{2^{10}} = 2;\]
\[3)\ \sqrt[3]{\sqrt[3]{9}} \bullet \sqrt[9]{3^{7}} = \sqrt[{3 \bullet 3}]{9} \bullet \sqrt[9]{3^{7}} =\]
\[= \sqrt[9]{9 \bullet 3^{7}} = \sqrt[9]{3^{2} \bullet 3^{7}} =\]
\[= \sqrt[9]{3^{9}} = 3;\]
\[4)\ \sqrt[4]{\sqrt[3]{25}} \bullet \sqrt[6]{5^{5}} = \sqrt[{4 \bullet 3}]{25} \bullet \sqrt[6]{5^{5}} =\]
\[= \sqrt[{2 \bullet 6}]{5^{2}} \bullet \sqrt[6]{5^{5}} = \sqrt[6]{5} \bullet \sqrt[6]{5^{5}} =\]
\[= \sqrt[6]{5^{6}} = 5.\]