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In number theory, an Euler product is an expansion of a Dirichlet series into an infinite product indexed by prime numbers. The name arose from the case of the Riemann zeta-function, where such a product representation was proved by Leonhard Euler. ==Definition== In general, if is a multiplicative function, then the Dirichlet series : is equal to : where the product is taken over prime numbers , and is the sum : In fact, if we consider these as formal generating functions, the existence of such a ''formal'' Euler product expansion is a necessary and sufficient condition that be multiplicative: this says exactly that is the product of the whenever factors as the product of the powers of distinct primes . An important special case is that in which is totally multiplicative, so that is a geometric series. Then : as is the case for the Riemann zeta-function, where , and more generally for Dirichlet characters. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Euler product」の詳細全文を読む スポンサード リンク
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