Exhaustive classification conjecture for universal diagonal ternary quadratic forms

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Let pp be a prime and let ℓ\ell satisfy 1≤ℓ<p1\leq\ell<p. A diagonal ternary positive quadratic form is (p,ℓ)(p,\ell)-universal if it represents every natural number congruent to ℓ\ell modulo pp. For a,b,c>0a,b,c>0, write ⟨a,b,c⟩\langle a,b,c\rangle for the form ax2+by2+cz2ax^2+by^2+cz^2.

Exhaustive classification conjecture. The complete list of diagonal ternary positive (p,ℓ)(p,\ell)-universal quadratic forms is the one displayed in the source, namely the forms listed for p=2,3,5,7p=2,3,5,7, and 101101 with (p,ℓ)=(101,98)(p,\ell)=(101,98).

The authors say that the computational data suggest that x2+2y2+101z2x^2+2y^2+101z^2 was the last missing example and that the displayed knowledge is exhaustive. This stronger classification claim is presented as conjectural and is not proved in the supplied text.

References

Primary source

Tomáš Hejda and Vítězslav Kala, “Ternary quadratic forms representing a given arithmetic progression”, arXiv:1906.02538 (2021).

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