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Dedekind psi function : ウィキペディア英語版
Dedekind psi function
In number theory, the Dedekind psi function is the multiplicative function on the positive integers defined by
: \psi(n) = n \prod_\left(1+\frac\right),
where the product is taken over all primes p dividing n (by convention, ψ(1) is the empty product and so has value 1). The function was introduced by Richard Dedekind in connection with modular functions.
The value of ψ(''n'') for the first few integers ''n'' is:
:1, 3, 4, 6, 6, 12, 8, 12, 12, 18, 12, 24 ... .
ψ(''n'') is greater than ''n'' for all ''n'' greater than 1, and is even for all ''n'' greater than 2. If ''n'' is a square-free number then ψ(''n'') = σ(''n'').
The ψ function can also be defined by setting ψ(pn) = (p+1)pn-1 for powers of any prime ''p'', and then extending the definition to all integers by multiplicativity. This also leads to a proof of the generating function in terms of the Riemann zeta function, which is
:\sum \frac = \frac.
This is also a consequence of the fact that we can write as a Dirichlet convolution of \psi= \mathrm
* |\mu| .
==Higher Orders==
The generalization to higher orders via ratios of Jordan's totient is
:\psi_k(n)=\frac
with Dirichlet series
:\sum_\frac = \frac.
It is also the Dirichlet convolution of a power and the square
of the Möbius function,
:\psi_k(n) = n^k
* \mu^2(n).
If
:\epsilon_2 = 1,0,0,1,0,0,0,0,1,0,0,0,0,0,0,1,0,0,0\ldots
is the characteristic function of the squares, another Dirichlet convolution
leads to the generalized σ-function,
:\epsilon_2(n)
* \psi_k(n) = \sigma_k(n).

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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