English

Ramanujan's continued fractions of order $10$ as modular functions

Number Theory 2025-06-12 v2

Abstract

We explore the modularity of the continued fractions I(τ),J(τ),T1(τ),T2(τ)I(\tau), J(\tau), T_1(\tau), T_2(\tau) and U(τ)=I(τ)/J(τ)U(\tau)=I(\tau)/J(\tau) of order 1010, where I(τ)I(\tau) and J(τ)J(\tau) are introduced by Rajkhowa and Saikia, which are special cases of certain identities of Ramanujan. In particular, we show that these fractions can be expressed in terms of an η\eta-quotient g(τ)g(\tau) that generates the field of all modular functions on the congruence subgroup Γ0(10)\Gamma_0(10). Consequently, we prove that modular equations for g(τ)g(\tau) and U(τ)U(\tau) exist at any level and derive these equations of prime levels p11p\leq 11. We also show that the continued fractions of order 1010 can be explicitly evaluated using a singular value of g(τ)g(\tau), which under certain conditions, generates the Hilbert class field of an imaginary quadratic field. We employ the methods of Lee and Park to establish our results.

Keywords

Cite

@article{arxiv.2404.05756,
  title  = {Ramanujan's continued fractions of order $10$ as modular functions},
  author = {Victor Manuel Aricheta and Russelle Guadalupe},
  journal= {arXiv preprint arXiv:2404.05756},
  year   = {2025}
}

Comments

21 pages; made minor changes as suggested by referees