

Redheffer's matrix

\end{rawhtml} The Redheffer matrix $A(n)$ is an $n\times n$ matrix of 0's and 1's defined by $A(i,j) = 1$ if $j = 1$ or if $i$ divides $j$, and $A(i,j) = 0$ otherwise. Redheffer proved that $A(n)$ has $ n-[n \log 2]-1$ eigenvalues equal to 1. Also, A has a real eigenvalue (the spectral radius) which is approximately $\sqrt(n)$, a negative eigenvalue which is approximately $-\sqrt{n}$ and the remaining eigenvalues are small. The Riemann hypothesis is true if and only if $\det(A) = O(n^{1/2+\epsilon})$ for every $\epsilon > 0$. Barrett Forcade, Rodney, and Pollington [ \begin{rawhtml} MR 89j:15029 \end{rawhtml}] give an easy proof of Redheffer's theorem. They also prove that the spectral radius of $A(n)$ is $=n^{1/2}+\tfrac 12\log n+O(1).$ See also the paper of Roesleren [ \begin{rawhtml} MR 87i:11111 \end{rawhtml}]. Vaughan [ \begin{rawhtml} MR 94b:11086 \end{rawhtml}] and [ \begin{rawhtml} MR 96m:11073 \end{rawhtml}] determines the dominant eigenvalues with an error term $O(n^{-2/3})$ and shows that the nontrivial eigenvalues are $\ll(\log n)^{2/5}$ (unconditionally), and $\ll\log\log(2+n)$ on Riemann's hypothesis. It is possible that the nontrivial eivenvalues lie in the unit disc. \begin{rawhtml}
