P511
projecteuler.net

Sequences with Nice Divisibility Properties

ℹ️Published on Saturday, 11th April 2015, 07:00 pm; Solved by 464;
Difficulty rating: 55%

Let $Seq(n,k)$ be the number of positive-integer sequences $\{a_i\}_{1 \le i \le n}$ of length $n$ such that:

  • $n$ is divisible by $a_i$ for $1 \le i \le n$, and
  • $n + a_1 + a_2 + \cdots + a_n$ is divisible by $k$.

Examples:

$Seq(3,4) = 4$, and the $4$ sequences are:
$\{1, 1, 3\}$
$\{1, 3, 1\}$
$\{3, 1, 1\}$
$\{3, 3, 3\}$

$Seq(4,11) = 8$, and the $8$ sequences are:
$\{1, 1, 1, 4\}$
$\{1, 1, 4, 1\}$
$\{1, 4, 1, 1\}$
$\{4, 1, 1, 1\}$
$\{2, 2, 2, 1\}$
$\{2, 2, 1, 2\}$
$\{2, 1, 2, 2\}$
$\{1, 2, 2, 2\}$

The last nine digits of $Seq(1111,24)$ are $840643584$.

Find the last nine digits of $Seq(1234567898765,4321)$.



Soluzione

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