15 and 7 short stories
There are 15 books in the series.
There are 15 books in the Secret Seven series by Enid Blyton, each featuring the adventures of a group of child detectives who solve mysteries together.
There are a lot of books by Enid Blyton, such as The Famous Five series, The Secret Seven series, The Five Find-Outers series, and many more. Like the Noddy series, some of which are reviewed here noddybooks.blogspot.com
There are a total of seven books in "The Unwanteds" series written by Lisa McMann.
There are seven in the first series, however the second series is still being published.
15 and 7 short stories
You can find free downloads of the Secret Seven books in the public domain on sites like Project Gutenberg or through libraries that offer eBooks for borrowing. However, please note that many of Enid Blyton's works are still under copyright, so be sure to check the copyright status before downloading.
7 seven
In the first series there are Seven books, however there are 2 or more books in the second series that I know of. The first two are Phoenix and Lion
The Secret Zoo is by Brian Chick. The book has 320 pages. It is the first book in a series of five books.
As of now there are 5 Found, Sent, Sabotaged, Torn, and Caught
There will be eithere four or five. The fourth one is still pretty new.