Debye function
From specialfunctionswiki
The Debye functions, $D_n$, are defined by $$D_n(x)=\dfrac{n}{x^n} \displaystyle\int_0^x \dfrac{t^n}{e^t-1} \mathrm{d}t.$$
The Debye functions, $D_n$, are defined by $$D_n(x)=\dfrac{n}{x^n} \displaystyle\int_0^x \dfrac{t^n}{e^t-1} \mathrm{d}t.$$