Eric Weisstein's World of Mathematics, <a href="httphttps://mathworld.wolfram.com/OddPart.html">Odd Part</a>
Eric Weisstein's World of Mathematics, <a href="httphttps://mathworld.wolfram.com/AperysConstant.html">Apery's constant</a>
Eric Weisstein's World of Mathematics, <a href="httphttps://mathworld.wolfram.com/RiemannZetaFunction.html">Riemann Zeta Function</a>