ProofWiki:Sandbox

Theorem
$\forall n \in \Z_{>0}: \displaystyle \sum_{k \mathop = 0}^{n} \binom {2n} {2k} E_{2n - 2k } = 0$

where $E_k$ denotes the $k$th Euler number.

Proof
Take the definition of Euler numbers:

From the definition of the exponential function:

Thus:

By Product of Absolutely Convergent Series, we will let:

Then:

$\forall n \in \Z_{\gt 0}$, term by term $c_n$ is equal to:

Grouping like even terms produces:

Multiplying $c_n$ through by $n!$ gives:

But those coefficients are the binomial coefficients:

Hence the result.

Also see

 * Sum of Bernoulli Numbers by Binomial Coefficients Vanishes