Tewodros Amdeberhan, Olivier R. Espinosa, Victor H. Moll, Armin Straub — American Mathematical Monthly — Volume 117, Number 15, 2010, Pages 618-632


One of the earliest examples of analytic representations for \(\pi\) is given by an infinite product provided by Wallis in 1655. The modern literature often presents this evaluation based on the integral formula $$ \frac{2}{\pi} \int_0^\infty \frac{dx}{(x^2+1)^{n+1}} = \frac{1}{2^{2n}} \binom{2n}{n}. $$ In trying to understand the behavior of this integral when the integrand is replaced by the inverse of a product of distinct quadratic factors, the authors encounter relations to some formulas of Ramanujan, expressions involving Schur functions, and Matsubara sums that have appeared in the context of Feynman diagrams.


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    author = {Tewodros Amdeberhan and Olivier R. Espinosa and Victor H. Moll and Armin Straub},
    title = {{Wallis-Ramanujan-Schur-Feynman}},
    journal = {American Mathematical Monthly},
    year = {2010},
    volume = {117},
    number = {15},
    pages = {618--632},
    doi = {10.4169/000298910X496741},