P467
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Superinteger

ℹ️Published on Sunday, 13th April 2014, 10:00 am; Solved by 491;
Difficulty rating: 50%

An integer $s$ is called a superinteger of another integer $n$ if the digits of $n$ form a subsequenceA subsequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements. of the digits of $s$.
For example, $2718281828$ is a superinteger of $18828$, while $314159$ is not a superinteger of $151$.

Let $p(n)$ be the $n$th prime number, and let $c(n)$ be the $n$th composite number. For example, $p(1) = 2$, $p(10) = 29$, $c(1)$ = 4 and $c(10) = 18$.
$\{p(i) : i \ge 1\} = \{2, 3, 5, 7, 11, 13, 17, 19, 23, 29, \dots\}$
$\{c(i) : i \ge 1\} = \{4, 6, 8, 9, 10, 12, 14, 15, 16, 18, \dots\}$

Let $P^D$ be the sequence of the digital roots of $\{p(i)\}$ ($C^D$ is defined similarly for $\{c(i)\}$):
$P^D = \{2, 3, 5, 7, 2, 4, 8, 1, 5, 2, \dots\}$
$C^D = \{4, 6, 8, 9, 1, 3, 5, 6, 7, 9, \dots\}$

Let $P_n$ be the integer formed by concatenating the first $n$ elements of $P^D$ ($C_n$ is defined similarly for $C^D$).
$P_{10} = 2357248152$
$C_{10} = 4689135679$

Let $f(n)$ be the smallest positive integer that is a common superinteger of $P_n$ and $C_n$.
For example, $f(10) = 2357246891352679$, and $f(100) \bmod 1\,000\,000\,007 = 771661825$.

Find $f(10\,000) \bmod 1\,000\,000\,007$.



Soluzione

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