P442
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Eleven-free Integers

ℹ️Published on Saturday, 26th October 2013, 01:00 pm; Solved by 443;
Difficulty rating: 60%

An integer is called eleven-free if its decimal expansion does not contain any substring representing a power of $11$ except $1$.

For example, $2404$ and $13431$ are eleven-free, while $911$ and $4121331$ are not.

Let $E(n)$ be the $n$th positive eleven-free integer. For example, $E(3) = 3$, $E(200) = 213$ and $E(500\,000) = 531563$.

Find $E(10^{18})$.



Soluzione

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