Actually read this some time ago (~46 years) while trying to figure out why I simply could not believe in Jesus or God or anything else I was being told by Bible Thumpers. I came to really like M.M. Mangasarian. This is a free ebook. You don't even need a reader app for it.
I do suggest getting the Gutenberg App from your phone's App Store. It will give you access to a large supply of free ebooks, many of which are classics