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Asymptotic identities for additive convolutions of sums of divisors

Published online by Cambridge University Press:  01 April 2022

ROBERT J. LEMKE OLIVER
Affiliation:
Department of Mathematics, Tufts University, 503 Boston Ave, Medford, MA 02155, U.S.A. e-mail: Robert.Lemke_Oliver@tufts.edu
SUNROSE T. SHRESTHA
Affiliation:
Department of Mathematics and Computer Science, Wesleyan University, 45 Wyllys Ave, Middletown, CT 06459, U.S.A. e-mail: sunrose.shrestha@gmail.com
FRANK THORNE
Affiliation:
Department of Mathematics, University of South Carolina, 1523 Greene St, Columbia, SC 29201, U.S.A. e-mail: thorne@math.sc.edu

Abstract

In a 1916 paper, Ramanujan studied the additive convolution $S_{a, b}(n)$ of sum-of-divisors functions $\sigma_a(n)$ and $\sigma_b(n)$ , and proved an asymptotic formula for it when a and b are positive odd integers. He also conjectured that his asymptotic formula should hold for all positive real a and b. Ramanujan’s conjecture was subsequently proved by Ingham, and then by Halberstam with a power saving error term.

In this paper, we give a new proof of Ramanujan’s conjecture that obtains lower order terms in the asymptotics for most ranges of the parameters. We also describe a connection to a counting problem in geometric topology that was studied in the second author’s thesis and which served as our initial motivation in studying this sum.

Type
Research Article
Copyright
© The Author(s), 2022. Published by Cambridge University Press on behalf of Cambridge Philosophical Society

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