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Infinite sum of the product of exponential and logarithmic functions, its analytic continuation, and application
Author(s) -
Yuk L. Yung,
Cameron Taketa,
Ross Cheung,
RunLie Shia
Publication year - 2009
Publication title -
discrete and continuous dynamical systems - b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 53
eISSN - 1553-524X
pISSN - 1531-3492
DOI - 10.3934/dcdsb.2010.13.229
Subject(s) - ramanujan's sum , analytic continuation , infinite product , riemann zeta function , mathematics , digamma function , combinatorics , gamma function , product (mathematics) , logarithm , riemann hypothesis , exponential function , series (stratigraphy) , logarithmic derivative , mathematical analysis , prime zeta function , arithmetic zeta function , paleontology , geometry , biology
We show that the function S_(1)(x) = ∑_(k=1)^∞ e^(-2πkx) log k can be expressed as the sum of a simple function and an infinite series, whose coefficients are related to the Riemann zeta function. Analytic continuation to the imaginary argument S_(1)(ix) = K_0(x) is made. For x = p/q where p and q are integers with p < q, closed finite sum expressions for K_0(p/q) and K_1(p/q) are derived. The latter results enable us to evaluate Ramanujan's function ψ(x) = ∑_(k=1)^∞ [(logk)/k - (log(k+x))/(k+x)] for x = -2/3, -3/4, and -5/6, confirming what Ramanujan claimed but did not explicitly reveal in his Notebooks. The interpretation of a pair of apparently inscrutable divergent series in the notebooks is discussed. They reveal hitherto unsuspected connections between Ramanujan's ψ(x), K_0(x), K_1(x), and the classical formulas of Gauss and Kummer for the digamma function

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