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Published online by Cambridge University Press: 12 May 2017
We introduce a new arithmetic function $a(n)$ defined to be the number of random multiplications by residues modulo
$n$ before the running product is congruent to zero modulo
$n$. We give several formulas for computing the values of this function and analyze its asymptotic behavior. We find that it is closely related to
$P_{1}(n)$, the largest prime divisor of
$n$. In particular,
$a(n)$ and
$P_{1}(n)$ have the same average order asymptotically. Furthermore, the difference between the functions
$a(n)$ and
$P_{1}(n)$ is
$o(1)$ as
$n$ tends to infinity on a set with density approximately
$0.623$. On the other hand, however, we see that (except on a set of density zero) the difference between
$a(n)$ and
$P_{1}(n)$ tends to infinity on the integers outside this set. Finally, we consider the asymptotic behavior of the difference between these two functions and find that
$\sum _{n\leqslant x}(a(n)-P_{1}(n))\sim (1-\unicode[STIX]{x1D70B}/4)\sum _{n\leqslant x}P_{2}(n)$, where
$P_{2}(n)$ is the second largest divisor of
$n$.