[離散] 亂序

For the positive integers 1,2,........,n , there are 11660 derangements where 1,2,3 4 and 5 appear
in the first five position. What is the value of n?


請問一下怎麼算，原本以為是D5 * Dn-5 = 11660
結果算出來不是整數.....


可以解釋一下題意嗎?? 謝謝