A mod 32 class-number congruence for quadratic fields of discriminants −8p-8p and 8p8p

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Let pp be a prime such that p≡3(mod4)p\equiv 3\pmod 4. Let h(−8p)h(-8p) and h(8p)h(8p) denote the class numbers associated with the discriminants −8p-8p and 8p8p, respectively, and let Ψ\Psi be the function used in the paper. Conjectural congruence. One has

h(−8p)≡h(8p)(Ψ(22p)3−Ψ(1+2p2)3)(mod32).h(-8p)\equiv h(8p)\left(\frac{\Psi(2\sqrt{2p})}{3}-\frac{\Psi\left(\frac{1+\sqrt{2p}}{2}\right)}{3}\right)\pmod{32}.

The authors report that this stronger congruence holds for every prime p≡3(mod4)p\equiv3\pmod4 with p≤1000p\leq1000, whereas the paper establishes a corresponding congruence modulo 1616. Its validity in general remains open.

References

Primary source

Jigu Kim and Yoshinori Mizuno, “Congruences on the class numbers of Q(2p) for p3 (mod 4) a prime”, arXiv:2210.02668 (2022).

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