Interval computation of Viswanath's constant (Q1597644)

\textit{D. Viswanath} [Math. Comput. 69, 1131-1155 (2000; Zbl 0983.11007)] has shown that the terms of the random Fibonacci sequences defined by \(t_1=t_2=1\) and \(t_n= \pm t_{n-1}\pm t_{n-2}\) for \(n>2\), where each \(\pm\) sign is chosen randomly, increase exponentially in the sense that \(\root n\of {|t_n|}\to 1.13198824\dots\) as \(n\to \infty\) with probability 1. Viswanath computed this approximation for this limit with floating-point arithmetic and provided a rounding-error analysis to validate his computer calculation. In this note, we show how to avoid this rounding-error analysis by using interval arithmetic.