Cody and Hillstrom (1967) gives minimax rational approximations for
for the ranges 
,
, 
; precision is variable.
Hart et al. (1968) gives minimax polynomial and rational approximations to
and in the intervals
, 
, 
; precision is
variable. Cody et al. (1973) gives minimax rational approximations
for 
for the ranges 
and
; precision is variable.
Luke (1969b) gives the coefficients to 20D for the Chebyshev-series
expansions of 
, 
,
, 
, 
, and the
first six derivatives of for . These
coefficients are reproduced in Luke (1975). Clenshaw (1962)
also gives 20D Chebyshev-series coefficients for and its
reciprocal for . See Luke (1975, pp. 22–23)
for additional expansions.
See Schmelzer and Trefethen (2007) for a survey of rational approximations to
various scaled versions of 
.
For rational approximations to 
see
Luke (1975, pp. 13–16).
