Exhaustive classification conjecture for universal diagonal ternary quadratic forms

Let pp be a prime and let \ell satisfy 1<p1\leq\ell<p. A diagonal ternary positive quadratic form is (p,)(p,\ell)-universal if it represents every natural number congruent to \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,)(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,)=(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.

Sources & referencesView supporting material

Primary source

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

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