Hudson's conjecture on completely multiplicative functions of length three

Let F2,3F_{2,3} denote the set of completely multiplicative functions f:N{1,1}f:\mathbb{N}\to\{-1,1\} whose maximal run of consecutive +1+1 values has length 33. For primes p{5,7,11,13,53}p\in\{5,7,11,13,53\}, let fp±f_p^{\pm} be the modified Legendre symbols defined by fp±(p)=(pp)f_p^{\pm}(p')=\left(\frac{p'}{p}\right) for ppp'\ne p and fp±(p)=±1f_p^{\pm}(p)=\pm1. Let g1,g2,g3g_1,g_2,g_3 be completely multiplicative functions with g1(p)=g2(p)=(1)(p1)/2g_1(p)=g_2(p)=(-1)^{(p-1)/2} for p2p\ne2, g1(2)=g2(2)=+1g_1(2)=-g_2(2)=+1, g3(p)=+1g_3(p)=+1 for p2p\ne2, and g3(2)=1g_3(2)=-1. Hudson's conjecture. The set F2,3F_{2,3} consists precisely of the 1313 functions F2,3=STF_{2,3}=S\cup T, where S={fp+:p{5,7,11,13,53}}{fp:p{5,7,11,13,53}}S=\{f_p^+:p\in\{5,7,11,13,53\}\}\cup\{f_p^-:p\in\{5,7,11,13,53\}\} and T={g1,g2,g3}T=\{g_1,g_2,g_3\}. This is a classification conjecture for the much more difficult length-three case; the supplied text gives no resolution status.

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Primary source

Oleksiy Klurman, Alexander P. Mangerel and Joni Teräväinen, “On Elliott's conjecture and applications”, arXiv:2304.05344 (2023).

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