FLINT3.7.0-dev
/

gr_generic_doublefac, gr_generic_doublefac_ui

Synopsis#include <flint/gr_special.h>
int gr_generic_doublefac(gr_ptr res, gr_srcptr x, gr_ctx_t ctx)source
int gr_generic_doublefac_ui(gr_ptr res, ulong n, gr_ctx_t ctx)source

Double factorials: (2k)!! = 2^k k! and (2k+1)!! = (2k+1)!/(2k)!!; for non-integer x the extension 2^{x/2} (\pi/2)^{(\cos(\pi x) - 1)/4} \Gamma(1 + x/2).

Cite this page

The FLINT team, “gr_generic_doublefac, gr_generic_doublefac_ui (gr_special.h),” FLINT: Fast Library for Number Theory, documentation, version 3.7.0-dev, 2026. https://flintlib.org/doc/gr_special/gr_generic_doublefac.html (generated 2026-10-20).