  Terpai [22] proved the Nordhaus-Gaddum bound that $\mu(G) + \mu(\overline{G})
\le 4n/3 - 1$, where $\mu(G)$ is the spectral radius of a graph $G$ with $n$
vertices. Let $s^+$ denote the sum of the squares of the positive eigenvalues
of $G$. We prove that $\sqrt{s^{+}(G)} + \sqrt{s^+(\overline{G})} < \sqrt{2}n$
and conjecture that $\sqrt{s^{+}(G)} + \sqrt{s^+(\overline{G})} \le 4n/3 - 1.$
We have used AutoGraphiX and Wolfram Mathematica to search for a
counter-example. We also consider Nordhaus-Gaddum bounds for $s^+$ and bounds
for the Randi\'c index.
