Approximation of values of hypergeometric functions by restricted rationals
Journal de théorie des nombres de Bordeaux, Volume 19 (2007) no. 2, pp. 393-404.

We compute upper and lower bounds for the approximation of hyperbolic functions at points 1/s (s=1,2,) by rationals x/y, such that x,y satisfy a quadratic equation. For instance, all positive integers x,y with y0(mod2) solving the Pythagorean equation x 2 +y 2 =z 2 satisfy

|ysinh(1/s)-x|loglogy logy.

Conversely, for every s=1,2, there are infinitely many coprime integers x,y, such that

|ysinh(1/s)-x|loglogy logy

and x 2 +y 2 =z 2 hold simultaneously for some integer z. A generalization to the approximation of h(e 1/s ) for rational functions h(t) is included.

Nous calculons des bornes supérieures et inférieures pour l’approximation de fonctions hyperboliques aux points 1/s (s=1,2,) par des rationnels x/y, tels que x,y satisfassent une équation quadratique. Par exemple, tous les entiers positifs x,y avec y0(mod2), solutions de l’équation de Pythagore x 2 +y 2 =z 2 , satisfont

|ysinh(1/s)-x|loglogy logy.

Réciproquement, pour chaque s=1,2,, il existe une infinité d’entiers x,y, premiers entre eux, tels que

|ysinh(1/s)-x|loglogy logy

et x 2 +y 2 =z 2 soient réalisés simultanément avec z entier. Une généralisation à l’approximation de h(e 1/s ), pour h(t) fonction rationnelle, est incluse.

DOI: 10.5802/jtnb.593
Elsner, Carsten 1; Komatsu, Takao 2; Shiokawa, Iekata 3

1 FHDW Hannover, University of Applied Sciences Freundallee 15 D-30173 Hannover, Germany
2 Faculty of Science and Technology Hirosaki University Hirosaki, 036-8561, Japan
3 Department of Mathematics Keio University Hiyoshi 3-14-1 Yokohama, 223-8522, Japan
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Elsner, Carsten; Komatsu, Takao; Shiokawa, Iekata. Approximation of values of hypergeometric functions by restricted rationals. Journal de théorie des nombres de Bordeaux, Volume 19 (2007) no. 2, pp. 393-404. doi : 10.5802/jtnb.593. http://archive.numdam.org/articles/10.5802/jtnb.593/

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