https://www.dlsite.com/maniax/work/=/product_id/RJ01234143.html
The original file names skipped 02 and 21. I'm not sure if this is a mistake or if the author deleted something. But it seems that there is no content missing.
不知道为什么买来就没有序号2和21，不过看内容好像没有缺失。

Thanks for uploading.
This book has 22 pages.
Page 02 is the inside front cover, and page 21 is the inside back cover.
Both are blank pages, so the author probably didn't include them.
https://ec.toranoana.jp/tora_r/ec/item/040031166930/

Base +6