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\[N_{\nu}={ 8 \pi\over{c^3}}\; {\nu^2\over{e^{x}-1}}\]
\[F_{\nu}={ 2 \pi\over{c^2}}\; {h \nu^3\over{e^{x}-1}}\]
\[N_{\lambda}={8 \pi}\;  {\lambda^{-4}\over{e^{x}-1}}\]
\[F_{\lambda}={2 \pi c}\; {hc \lambda^{-5}\over{e^{x}-1}}\]
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