Don't know if you're working with complex numbers, but in the real case we have
How would I go about computing the series expansion of 1/cosh(z), or at least the first few terms? I know the series of cosh(z), but trying to manipulate that, or trying to form it using the e^z definition of cosh, always gives me something complicated and looking very far away from a term-by-term definition.
Any thoughts?