Discriminator conjecture for half-integer quadratic sequences with coefficient ratio divisible by 3

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Let bb and cc be non-zero integers such that 3∤bc3\nmid bc. For a sequence

(qr⁡(n))n≥0=(3c2n2+bc2n)n≥0,(\operatorname{qr}(n))_{n\geq 0}=\left(\frac{3c}{2}n^2+\frac{bc}{2}n\right)_{n\geq 0},

let Dqr⁡(n)D_{\operatorname{qr}}(n) denote its discriminator, the least modulus for which the first nn sequence values are pairwise distinct. The discriminator conjecture. For every such sequence, there exists at least one value of n≥1n\geq 1 such that

Dqr⁡(n)≠3⌈log⁡3n⌉.D_{\operatorname{qr}}(n)\ne 3^{\lceil\log_3 n\rceil}.

The preceding result rules out the claimed discriminator formula in most cases of half-integer quadratic coefficients; this conjecture concerns the remaining case in which the quadratic coefficient is 3c/23c/2, with 3∤c3\nmid c and c∣β′c\mid\beta' as represented by the linear coefficient bc/2bc/2. The authors report that they were unable to find any examples satisfying the formula, but the conjecture remains open.

References

Primary source

Sajed Haque, “Quadratic sequences with prime power discriminators”, arXiv:2209.03265 (2022).

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