Function: bernfrac
Section: transcendental
C-Name: bernfrac
Prototype: L
Help: bernfrac(x): Bernoulli number B_x, as a rational number.
Doc: Bernoulli number\sidx{Bernoulli numbers} $B_x$,
 where $B_0=1$, $B_1=-1/2$, $B_2=1/6$,\dots, expressed as a rational number.
 The argument $x$ should be of type integer.
