Computes \zeta(s) - 1 for integer n, n \ne 1, where \zeta denotes the Riemann zeta function.
See also: gsl_sf_zetam1, gsl_sf_zeta, gsl_sf_zeta_int.
err contains an estimate of the absolute error in the value z.
This function is from the GNU Scientific Library, see http://www.gnu.org/software/gsl/ for documentation.
Package: gsl