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von mangoldt function

n. (context math English) A certain arithmetic function that is neither multiplicative nor additive. It is denoted by Λ(''n'') and defined as :Lambda(n) = begin{cases} log p & mbox{if }n=p^k mbox{ for some prime } p mbox{ and integer } k ge 1, 0 & mbox{otherwise.} end{cases}

Wikipedia
Von Mangoldt function

In mathematics, the von Mangoldt function is an arithmetic function named after German mathematician Hans von Mangoldt. It is an example of an important arithmetic function that is neither multiplicative nor additive.