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→Examples: Added Unitary divisor as example which is referenced lower down. Tags: Mobile edit Mobile web edit |
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** ''σ''<sub>0</sub>(''n'') = ''d''(''n'') the number of positive [[divisor]]s of ''n'',
** ''σ''<sub>1</sub>(''n'') = ''σ''(''n''), the sum of all the positive divisors of ''n''.
*The sum of the ''k''-th [[exponentiation|powers]] of the [[Unitary divisor]]s is denoted by σ*<sub>''k''</sub>(''n''):
:<math>\sigma_k^*(n) = \sum_{d \,\mid\, n \atop \gcd(d,\,n/d)=1} \!\! d^k.</math>
* ''a''(''n''): the number of non-isomorphic abelian groups of order ''n''.
* ''λ''(''n''): the [[Liouville function]], ''λ''(''n'') = (−1)<sup>Ω(''n'')</sup> where Ω(''n'') is the total number of primes (counted with multiplicity) dividing ''n''. (completely multiplicative).
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