Read this book sometime in the early 2010's, but it was probably written back in the 2000's. I recall it being a kid/young-adult Christian fiction fantasy series that had maybe 4-5 books in the series. The reading level was probably middle school/high school range.
It starts with a boy and his sister visiting a weird library after closing hours and the sister disappears as the books start talking on the shelves to the boy. The boy asks them where his sister went and one of the books confesses that she went into the book because a shadowy evil being made it lie to her and said it could make her smarter with math numbers. The boy goes into the same book and enters a weird realm of magic wher



