Conjecture on Euler liars and Carmichael or Sophie Germain pseudoprimes

Let nn be an odd squarefree composite integer, and let Euler liars in Zn\mathbb{Z}_n^* mean the elements aa satisfying the Euler probable-prime congruence a(n1)/2(an)(modn)a^{(n-1)/2}\equiv \left(\frac{a}{n}\right)\pmod n. Euler-liar count conjecture. If nn has φ(n)/2\varphi(n)/2 Euler liars in Zn\mathbb{Z}_n^*, then nn is a Carmichael number; and if it has φ(n)/4\varphi(n)/4 Euler liars in Zn\mathbb{Z}_n^*, then nn is either a Carmichael number or a Sophie Germain pseudoprime. The claim proposes a classification of odd squarefree composites with especially many Euler liars; its resolution is left as future work in the source.

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Primary source

Alejandra Alcantarilla Sánchez, Jolijn Cottaar, Tanja Lange and Benne de Weger, “Ours go to 211: Euler pseudoprimes to 47 prime bases (from Carmichael numbers)”, arXiv:2602.21840 (2026).

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