Dirichlet convolution

That can’t be right I was skimming a book on number theory [1] recently and came across the following theorem that makes no sense out of context: An arithmetical function f has an inverse if and only if f(1) ≠ 0. Wait, what?! That’s obviously false unless I’ve missed something. Maybe “arithmetical function” is far […] The post Dirichlet convolution first appeared on John D. Cook....

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