Gessel, Ira M., and Larcombe, Peter J. “The Sum 16nΣ2nk=04k( 1/2k)(-1/2k)(-2k 2n-k): A Third Proof of Its Closed Form”. Utilitas Mathematica 80 (September 9, 2009). Accessed May 8, 2026. https://utilitasmathematica.com/index.php/Index/article/view/596.