English

Congruences on the class numbers of $\mathbb{Q}(\sqrt{\pm 2p})$ for $p\equiv3$ $(\text{mod }4)$ a prime

Number Theory 2022-10-07 v1

Abstract

For a prime p3p\equiv 3 (mod 4)(\text{mod }4), let h(8p)h(-8p) and h(8p)h(8p) be the class numbers of Q(2p)\mathbb{Q}(\sqrt{-2p}) and Q(2p)\mathbb{Q}(\sqrt{2p}), respectively. Let Ψ(ξ)\Psi(\xi) be the Hirzebruch sum of a quadratic irrational ξ\xi. We show that h(8p)h(8p)(Ψ(22p)/3Ψ((1+2p)/2)/3)h(-8p)\equiv h(8p)\Big(\Psi(2\sqrt{2p})/3-\Psi\big((1+\sqrt{2p})/2\big)/3\Big) (mod 16)(\text{mod }16). Also, we show that h(8p)2h(8p)Ψ(22p)/3h(-8p)\equiv 2h(8p)\Psi(2\sqrt{2p})/3 (mod 8)(\text{mod }8) if p3p\equiv 3 (mod 8)(\text{mod }8), and h(8p)(2h(8p)Ψ(22p)/3)+4h(-8p)\equiv \big(2h(8p)\Psi(2\sqrt{2p})/3\big)+4 (mod 8)(\text{mod }8) if p7p\equiv 7 (mod 8)(\text{mod }8).

Keywords

Cite

@article{arxiv.2210.02668,
  title  = {Congruences on the class numbers of $\mathbb{Q}(\sqrt{\pm 2p})$ for $p\equiv3$ $(\text{mod }4)$ a prime},
  author = {Jigu Kim and Yoshinori Mizuno},
  journal= {arXiv preprint arXiv:2210.02668},
  year   = {2022}
}

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16 pages