ABC implies that Ramanujan's tau function misses almost all primes

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Main Authors: Angdinata, David Kurniadi, Chen, Evan, Cummins, Chris, Eltschig, Ben, Grubisic, Dejan, Haller, Leopold, Hong, Letong, Kurghinyan, Andranik, Lau, Kenny, Leather, Hugh, Lee, Seewoo, Mahns, Simon, Markosyan, Aram H., Muddana, Rithikesh, Ono, Ken, Patel, Manooshree, Pendharkar, Gaurang, Rathi, Vedant, Schneidman, Alex, Seeker, Volker, Sengupta, Shubho, Sinha, Ishan, Xin, Jimmy, Zhang, Jujian
Format: Preprint
Published: 2026
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author Angdinata, David Kurniadi
Chen, Evan
Cummins, Chris
Eltschig, Ben
Grubisic, Dejan
Haller, Leopold
Hong, Letong
Kurghinyan, Andranik
Lau, Kenny
Leather, Hugh
Lee, Seewoo
Mahns, Simon
Markosyan, Aram H.
Muddana, Rithikesh
Ono, Ken
Patel, Manooshree
Pendharkar, Gaurang
Rathi, Vedant
Schneidman, Alex
Seeker, Volker
Sengupta, Shubho
Sinha, Ishan
Xin, Jimmy
Zhang, Jujian
author_facet Angdinata, David Kurniadi
Chen, Evan
Cummins, Chris
Eltschig, Ben
Grubisic, Dejan
Haller, Leopold
Hong, Letong
Kurghinyan, Andranik
Lau, Kenny
Leather, Hugh
Lee, Seewoo
Mahns, Simon
Markosyan, Aram H.
Muddana, Rithikesh
Ono, Ken
Patel, Manooshree
Pendharkar, Gaurang
Rathi, Vedant
Schneidman, Alex
Seeker, Volker
Sengupta, Shubho
Sinha, Ishan
Xin, Jimmy
Zhang, Jujian
contents Lehmer conjectured that Ramanujan's tau-function never vanishes. In a related direction, a folklore conjecture asserts that infinitely many primes arise as absolute values of Ramanujan's tau-function. Recently, Xiong showed that these prime values form a subset of the primes with density at most $2/11$. Assuming the $abc$ Conjecture, we prove the stronger upper bound \[ S(X):=\#\{\ell\le X:\ \ell\ \text{prime and } |τ(n)|=\ell \text{ for some } n\ge 1\} = O(X^{13/22}), \] which implies that Ramanujan's tau-function misses a density 1 subset of the primes. We give a heuristic suggesting that $S(X)$ should nevertheless be infinite, with predicted order of magnitude \[ S(X)\asymp \frac{C X^{\frac{1}{11}}}{(\log X)^2}. \] The main engine in this note was formalized and produced automatically in Lean/Mathlib by AxiomProver from a natural-language statement of the problem.
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id arxiv_https___arxiv_org_abs_2603_29970
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle ABC implies that Ramanujan's tau function misses almost all primes
Angdinata, David Kurniadi
Chen, Evan
Cummins, Chris
Eltschig, Ben
Grubisic, Dejan
Haller, Leopold
Hong, Letong
Kurghinyan, Andranik
Lau, Kenny
Leather, Hugh
Lee, Seewoo
Mahns, Simon
Markosyan, Aram H.
Muddana, Rithikesh
Ono, Ken
Patel, Manooshree
Pendharkar, Gaurang
Rathi, Vedant
Schneidman, Alex
Seeker, Volker
Sengupta, Shubho
Sinha, Ishan
Xin, Jimmy
Zhang, Jujian
Number Theory
11F11 (Primary), 11F30 (Secondary)
Lehmer conjectured that Ramanujan's tau-function never vanishes. In a related direction, a folklore conjecture asserts that infinitely many primes arise as absolute values of Ramanujan's tau-function. Recently, Xiong showed that these prime values form a subset of the primes with density at most $2/11$. Assuming the $abc$ Conjecture, we prove the stronger upper bound \[ S(X):=\#\{\ell\le X:\ \ell\ \text{prime and } |τ(n)|=\ell \text{ for some } n\ge 1\} = O(X^{13/22}), \] which implies that Ramanujan's tau-function misses a density 1 subset of the primes. We give a heuristic suggesting that $S(X)$ should nevertheless be infinite, with predicted order of magnitude \[ S(X)\asymp \frac{C X^{\frac{1}{11}}}{(\log X)^2}. \] The main engine in this note was formalized and produced automatically in Lean/Mathlib by AxiomProver from a natural-language statement of the problem.
title ABC implies that Ramanujan's tau function misses almost all primes
topic Number Theory
11F11 (Primary), 11F30 (Secondary)
url https://arxiv.org/abs/2603.29970