How can you find the Eulers numbers in a power series expansion of secant in complex variable?

Answer 1

To find Euler's numbers in the power series expansion of the secant function, ( \sec(z) ), you start with its Taylor series representation around ( z = 0 ), given by ( \sec(z) = \sum_{n=0}^{\infty} E_n \frac{z^{2n}}{(2n)!} ), where ( E_n ) are the Euler numbers. The even-indexed coefficients ( E_n ) can be computed by differentiating ( \sec(z) ) at zero or by using combinatorial identities that relate to the Euler numbers. Specifically, you can extract the coefficients of ( z^{2n} ) in the expansion to identify the Euler numbers directly.