 In particular, the methods of zeta function regularization and Ramanujan summation assign the series a value of , which is expressed by a famous formula,
where the left-hand side has to be interpreted as being the value obtained by using one of the aforementioned summation methods and not as the sum of an infinite series in its usual meaning.These methods have applications in other fields such as complex analysis, quantum field theory, and string theory.In a monograph on moonshine theory, Terry Gannon calls this equation "one of the most remarkable formulae in science".