# How can I get the coefficient of a Dirichlet series?

Hello.

Let's see this example.

```
g(x)=(1-3^(-x))*(f(x))^2
```

where f(x) is the Riemann zeta function and x is complex variable.

If Re(s) is sufficiently large then g(x) is converges.

We only view this g(x) as a formal Dirichlet series.

What I want is coefficients.

The Riemann zeta function is rewritten by

```
f(x)=1+2^(-x)+3^(-x)+ ...
```

We can also rewrite the g(x) by the sum of `a_n * n^(-x)`

.

```
g(x)=sum{a_n * n^(-x) | n=1,2,...}
```

For given `n`

, how can I get `a_n`

??

Is there any helpful sage command ??

Thanks.

It's not a power series, it's a Dirichlet series, see https://en.wikipedia.org/wiki/Dirichl...

I see. I edited the title. Thanks.