The gamma-function tag has no usage guidance.

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**2**answers

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### Simplifying the expression involving instances of Gamma function

Is it possible to simplify the following expression involving instances of Gamma function:
$$E(p)=\frac{\frac{\Gamma(\frac{p+1}{2})}{\Gamma(\frac{p+2}{2})}}
{\left(\frac{\Gamma(\frac{p+1}{p})^2}{\...

**0**

votes

**1**answer

676 views

### Calculate conditional expectation of log(x) with gamma density

How to calculate the following expression:
$$\int_0^u{\ln(x)x^{k-1}e^{-x}}\;dx$$
As I know,
$$\int_0^\infty{\ln(x)x^{k-1}e^{-x}}dx = \Gamma(k)\Psi(k)$$
Are there any way to transfer the integral ...

**3**

votes

**0**answers

163 views

### Iterated Kumaraswamy distributions

The Kumaraswamy distribution has cdf $F(x;a,b) = 1-(1-x^a)^b$.
Does anyone know any formulas or properties relating to iterations of this on itself, meaning
$$ F_i(x;a,b) = 1-(1-F_{i-1}^a)^b$$
If ...

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vote

**3**answers

573 views

### Undefined gamma function problem

Hello,
I'm trying to solve the following integral :
$\int_0^\infty \frac{1}{t^{d/2}}(e^{-\gamma t} - e^{-\delta t})dt$.
I know it equals
$\Gamma(1-\frac{d}{2})[\gamma^{\frac{d}{2}-1}-\delta^{\...

**5**

votes

**5**answers

735 views

### Summation of an expression

Hi,
Does anyone have an idea about an exact or approximate formulae for the following summation?
$$
\sum_{j=1}^n \frac{j^k}{(j-1)!}
$$
where k is a positive integer (the denominator of the j^th term ...

**0**

votes

**1**answer

858 views

### Generalizations of a product formula for the gamma function

Hello and Happy holidays.
I am interested in generalizations of the following product formula for the gamma function
$\Gamma(z)= \int_{0}^{\infty} t^{z-1}e^{-t}dt$ when $n \geq 2$:
\begin{align}
\...

**2**

votes

**1**answer

633 views

### What are conditions to make f(x) defined by f(x)=f(x-1)*x + 1/e unique(for instance convex)?

[Background:]
Looking at the powerseries for the gamma-function
$ \Gamma(1+x) = 1 + a_1 x + a_2 x^2 - a_3 * x^3 + ... $
then we can arrive at a decomposition
$ \Gamma(1+x) = r(x) + g(x) $
...

**3**

votes

**1**answer

620 views

### Connection between Bernoulli polynomials and polygamma function

There is an intricate connection between Hurwitz Zeta and the (traditional) polygamma function:
$$\psi_n(z)=(-1)^{n+1}n!\zeta(n+1,z)$$
If to use a generalization for Bernoulli numbers, this can be ...

**2**

votes

**0**answers

368 views

### Can any antidifference (indefinite sum) of a function be expressed in elementary functions and generalized polygamma function if its integral can be expressed in elementary functions?

If the integral or multiplicative integral of a function can be expressed with elementary functions, does it mean its indefinite sum (antidifference) or indefinite product respectively can be ...

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votes

**2**answers

1k views

### Multiplicative integral of $\Gamma(x)$

A recent question on the notion and notation of multiplicative integrals
( What is the standard notation for a multiplicative integral? ) induced me to play with the Riemann products of the Gamma ...

**14**

votes

**2**answers

2k views

### Importance of Log Convexity of the Gamma Function

The Bohr-Mollerup theorem states that the Gamma function is the unique function that satisfies:
1) f(x+1) = x*f(x)
2) f(1) = 1
3) ln(f(x)) is convex
The Gamma function is meant to interpolate the ...

**84**

votes

**10**answers

11k views

### Why is the Gamma function shifted from the factorial by 1?

I've asked this question in every math class where the teacher has introduced the Gamma function, and never gotten a satisfactory answer. Not only does it seem more natural to extend the factorial ...

**8**

votes

**1**answer

1k views

### Errata for Emil Artin's 'The Gamma Function'?

In the English translation of The Gamma Function by Emil Artin (1964 - Holt, Rinehart and Winston) there appears to be a mistake in the formula given for the gamma function on page 24:
$$\Gamma(x) = \...

**3**

votes

**3**answers

500 views

### Reference request for a “well-known identity” in a paper of Shepp and Lloyd

I ran into a "well-known identity" on page 345 of Shepp and Lloyd's On ordered cycle lengths in a random permutation:
$$\int_x^{\infty} \frac{\exp(-y)}y dy = \int_0^x \frac{1-\exp(-y)}y dy - \log x - \...

**4**

votes

**2**answers

544 views

### Generalized binomial coefficients and Gaussian density

I ran into an expression calculating the expected value of $\exp(i t \sigma)$ where $\sigma$ is the total number of cycles in a uniformly chosen $S_n$ element. The expression is
$$E_n (\exp(i t \...

**2**

votes

**2**answers

1k views

### Hadamard's Gamma function

Hi, I'm looking for a link to a derivation of some of the basic properties of Hadamard's Gamma function. For instance that it satisfies $H(x+1)=xH(x)+\frac{1}{\Gamma(1-x)}$ I've been looking on the ...

**14**

votes

**2**answers

2k views

### Why does the Gamma function satisfy a functional equation?

In question #7656, Peter Arndt asked why the Gamma function completes the Riemann zeta function in the sense that it makes the functional equation easy to write down. Several of the answers were from ...

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votes

**1**answer

742 views

### Gamma function versions of combinatorial identites?

We can extend the binomial coefficient $\binom{n}{k}$ to $\mathbb{R}$ or $\mathbb{C}$ by defining $\binom{x}{y}=\frac{\Gamma(x+1)}{\Gamma(y+1)\Gamma(x-y+1)}$. Do any the standard binomial coefficient ...

**8**

votes

**3**answers

869 views

### No simple duplication formula for factorials?

Many special functions including the gamma function have a duplication formula of some sorts. In the case of the gamma function it reads:
Gamma(2z) = Gamma(z) Gamma(z+1/2) 22z-1/Gamma(1/2)
On ...