Catalan's Constant [Ramanujan's Formula] is a fascinating book by Holly Fee and Greg Fee that examines the phenomenal mathematical constant known as the Catalan Constant. The authors trace the history of the study of this constant, and also present a revolutionary formula discovered by the Indian mathematician Srinivasa Ramanujan. The book will help readers better understand complex mathematical concepts, as well as feel the excitement of discovering new and amazing mathematical worlds.