Currently available on:

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Amazon.com

Apple Books (iTunes)

Baker & Taylor

Barnes & Noble

Bibliotheca

Bookmate.com

Chinese Ebook Stores

ciando.com

dibook.hu

Dreame

Ekonyv.hu

Empik Group

Everand

Gardners.com

Google Play Books

Hoopla

Kobo

Kobo Plus

Mackin.com

Odilo.es

overdrive.com

Perlego

Storytel

Tolino and German network