ReplaceAll[((-BernoulliB[2n] (2n+2)(2n+1)(2^{2n+2}-4)(3^{2n+2}-9)(5^{2n+2}-25)(7^{2n+2}-49))/(4BernoulliB[2n+2] (2^{2n+2}-1)(3^{2n+2}-1)(5^{2n+2}-1)(7^{2n+2}-1)))^(1/2), {n -> 50}]