Ramanujan-type series for $\frac {1}{\pi }$, revisited
Canadian mathematical bulletin, Tome 67 (2024) no. 2, pp. 350-368
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In this note, we revisit Ramanujan-type series for $\frac {1}{\pi }$ and show how they arise from genus zero subgroups of $\mathrm {SL}_{2}(\mathbb {R})$ that are commensurable with $\mathrm {SL}_{2}(\mathbb {Z})$. As illustrations, we reproduce a striking formula of Ramanujan for $\frac {1}{\pi }$ and a recent result of Cooper et al., as well as derive a new rational Ramanujan-type series for $\frac {1}{\pi }$. As a byproduct, we obtain a Clausen-type formula in some general sense and reproduce a Clausen-type quadratic transformation formula closely related to the aforementioned formula of Ramanujan.
Mots-clés :
Orbifold uniformizations, 1⁄π, Clausen-type transformations
Ye, Dongxi. Ramanujan-type series for $\frac {1}{\pi }$, revisited. Canadian mathematical bulletin, Tome 67 (2024) no. 2, pp. 350-368. doi: 10.4153/S0008439523000772
@article{10_4153_S0008439523000772,
author = {Ye, Dongxi},
title = {Ramanujan-type series for $\frac {1}{\pi }$, revisited},
journal = {Canadian mathematical bulletin},
pages = {350--368},
year = {2024},
volume = {67},
number = {2},
doi = {10.4153/S0008439523000772},
url = {http://geodesic.mathdoc.fr/articles/10.4153/S0008439523000772/}
}
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