Equidistribution conjecture for the signs of square-free representation differences

From papers

For each odd square-free integer tt, let Δ(t)=rQ1(t)rQ2(t)\Delta(t)=r_{Q_1}(t)-r_{Q_2}(t), and define

N+(X)=#{tX:t is odd and square-free, Δ(t)>0},N_+(X)=\#\{t\leq X:t\text{ is odd and square-free},\ \Delta(t)>0\}, N(X)=#{tX:t is odd and square-free, Δ(t)<0},N_-(X)=\#\{t\leq X:t\text{ is odd and square-free},\ \Delta(t)<0\},

and N0(X)=N+(X)+N(X)N_{\ne 0}(X)=N_+(X)+N_-(X). Sign equidistribution conjecture. As XX\to\infty,

N+(X)N0(X)12,N(X)N0(X)12.\frac{N_+(X)}{N_{\ne 0}(X)}\longrightarrow\frac12,\qquad \frac{N_-(X)}{N_{\ne 0}(X)}\longrightarrow\frac12.

Equivalently, N+(X)N(X)N_+(X)\sim N_-(X). The numerical data suggest that the two signs of the difference of the representation numbers occur equally often among odd square-free integers for which the difference is nonzero; the preceding theorem gives quantitative lower bounds for both signs, but does not establish this equidistribution.

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Sources & referencesView supporting material

Primary source

Wei Tao and Guo Xuejun, “Signs of Square-Free Fourier Coefficients of Half-Integral weight cusp forms and the Congruent Number Problem”, arXiv:2607.24263 (2026).

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