The FunctionAdvisor(function_classes) command returns all class names for which information is available.

$\mathrm{FunctionAdvisor}\left(\mathrm{function\_classes}\right)$

$\left[\mathrm{trig}\,\mathrm{trigh}\,\mathrm{arctrig}\,\mathrm{arctrigh}\,\mathrm{elementary}\,\mathrm{GAMMA\_related}\,\mathrm{Psi\_related}\,\mathrm{Kelvin}\,\mathrm{Airy}\,\mathrm{Hankel}\,\mathrm{Bessel\_related}\,\mathrm{0F1}\,\mathrm{orthogonal\_polynomials}\,\mathrm{Ei\_related}\,\mathrm{erf\_related}\,\mathrm{Kummer}\,\mathrm{Whittaker}\,\mathrm{Cylinder}\,\mathrm{1F1}\,\mathrm{Elliptic\_related}\,\mathrm{Legendre}\,\mathrm{Chebyshev}\,\mathrm{2F1}\,\mathrm{Lommel}\,\mathrm{Struve\_related}\,\mathrm{hypergeometric}\,\mathrm{Jacobi\_related}\,\mathrm{InverseJacobi\_related}\,\mathrm{Elliptic\_doubly\_periodic}\,\mathrm{Weierstrass\_related}\,\mathrm{Zeta\_related}\,\mathrm{complex\_components}\,\mathrm{piecewise\_related}\,\mathrm{Other}\,\mathrm{Bell}\,\mathrm{Heun}\,\mathrm{Appell}\,\mathrm{trigall}\,\mathrm{arctrigall}\,\mathrm{Polylog\_related}\,\mathrm{integral\_transforms}\right]$

$\mathrm{FunctionAdvisor}\left(\mathrm{class\_members}\,\mathrm{elementary}\right)$

The 26 functions in the "elementary" class are:

$\left[\arccos \,\mathrm{arccosh}\,\mathrm{arccot}\,\mathrm{arccoth}\,\mathrm{arccsc}\,\mathrm{arccsch}\,\mathrm{arcsec}\,\mathrm{arcsech}\,\arcsin \,\mathrm{arcsinh}\,\arctan \,\mathrm{arctanh}\,\cos \,\cosh \,\cot \,\coth \,\csc \,\mathrm{csch}\,\exp \,\ln \,\sec \,\mathrm{sech}\,\sin \,\sinh \,\tan \,\tanh \right]$

$\mathrm{FunctionAdvisor}\left(\mathrm{class\_members}\,\mathrm{ortho}\right)$

* Partial match of "ortho" against topic "orthogonal_polynomials".
The 7 functions in the "orthogonal_polynomials" class are:

$\left[\mathrm{ChebyshevT}\,\mathrm{ChebyshevU}\,\mathrm{GegenbauerC}\,\mathrm{HermiteH}\,\mathrm{JacobiP}\,\mathrm{LaguerreL}\,\mathrm{LegendreP}\right]$

$\mathrm{FunctionAdvisor}\left(\mathrm{classify}\,\mathrm{Gegen}\right)$

* Partial match of "classify" against topic "classify_function".
* Partial match of Gegen against topic GegenbauerC.
GegenbauerC belongs to the subclass "orthogonal_polynomials" of the class "2F1" and so, in principle, it can be related to various of the 26 functions of those classes - see FunctionAdvisor( "orthogonal_polynomials" ); and FunctionAdvisor( "2F1" );

$\mathrm{orthogonal\_polynomials},\mathrm{2F1}$