Solution
= Solution
For state $n\geq1$, births occur at rate $\lambda$ and departures at rate
$$
d_n=\mu+(n-1)\delta.
$$
The birth--death detailed-balance weights are
$$
\pi_n=\pi_0\frac{\lambda^n}{\mu(\mu+\delta)\cdots(\mu+(n-1)\delta)}.
$$
Their ratios tend to zero, so the <series> is summable and normalization gives an invariant probability distribution.