Antiderivative of cosine integral
From specialfunctionswiki
Theorem
The following formula holds: $$\displaystyle\int \mathrm{Ci}(z) \mathrm{d}z = z \mathrm{Ci}(z) - \sin(z) + C,$$ where $\mathrm{Ci}$ denotes the cosine integral and $\sin$ denotes sine.
