Gessel, Ira M., & Larcombe, Peter J. (2009). The sum 16nΣ2nk=04k( 1/2k)(-1/2k)(-2k 2n-k): A third proof of its closed form. Utilitas Mathematica, 80. Retrieved from https://utilitasmathematica.com/index.php/Index/article/view/596