We can use the relationship between \( K_p \) and \( K_c \) for ideal gases:
\[
K_p = K_c \left( RT \right)^{\Delta n}
\]
where \( \Delta n \) is the change in the number of moles of gas, \( R = 0.0821 \, \text{L·atm/mol·K} \), and \( T = 400 + 273 = 673 \, \text{K} \). After calculating \( \Delta n \), we find that the value of \( K_p \) is \( 1.64 \times 10^{-6} \).
Final Answer:
\[
\boxed{1.64 \times 10^{-6}}
\]