Find the remainder when `sum_(r=1)^(n)r!` is divided by 15, if `n ge5`.

Explanation

To find the remainder when the sum \( \sum_{r=1}^{n} r! \) is divided by 15 for \( n \geq 5 \), we can follow these steps:

### Step 1: Write out the sum of factorials
The sum can be expressed as:
\[ S = 1! + 2! + 3! + 4! + 5! + 6! + \ldots + n! \]

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