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→Multiplicative and additive functions: fixed definitions of multiplicative and completely multiplicative arithmetic functions: we must require a(1) = 1, and the linked Wikipedia page points that out already. |
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An arithmetic function ''a'' is
* '''[[Completely additive function|completely additive]]''' if ''a''(''mn'') = ''a''(''m'') + ''a''(''n'') for all natural numbers ''m'' and ''n'';
* '''[[Completely multiplicative function|completely multiplicative]]''' if ''a''(1) = 1 and ''a''(''mn'') = ''a''(''m'')''a''(''n'') for all natural numbers ''m'' and ''n'';
Two whole numbers ''m'' and ''n'' are called [[coprime]] if their [[greatest common divisor]] is 1, that is, if there is no [[prime number]] that divides both of them.
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Then an arithmetic function ''a'' is
* '''[[Additive function|additive]]''' if ''a''(''mn'') = ''a''(''m'') + ''a''(''n'') for all coprime natural numbers ''m'' and ''n'';
* '''[[Multiplicative function|multiplicative]]''' if ''a''(1) = 1 and ''a''(''mn'') = ''a''(''m'')''a''(''n'') for all coprime natural numbers ''m'' and ''n''.
== Notation ==
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