ArithmeticGeometricMean[a, b] gives the arithmetic-geometric mean of a and b.
BesselJ
(Built-in Mathematica Symbol) BesselJ[n, z] gives the Bessel function of the first kind J_n (z).
Ceiling
(Built-in Mathematica Symbol) Ceiling[x] gives the smallest integer greater than or equal to x. Ceiling[x, a] gives the smallest multiple of a greater than or equal to x.
n!! gives the double factorial of n.
FixedPoint[f, expr] starts with expr, then applies f repeatedly until the result no longer changes.
GCD
(Built-in Mathematica Symbol) GCD[n_1, n_2, ...] gives the greatest common divisor of the n_i.
GegenbauerC[n, m, x] gives the Gegenbauer polynomial C_n^(m)(x). GegenbauerC[n, x] gives the renormalized form lim_(m->0) C_n^(m)(x)/m.
Hypergeometric1F1[a, b, z] is the Kummer confluent hypergeometric function \[Null]_1 F_1 (a; b; z).
LaguerreL[n, x] gives the Laguerre polynomial L_n (x). LaguerreL[n, a, x] gives the generalized Laguerre polynomial L_n^a(x).
LCM
(Built-in Mathematica Symbol) LCM[n_1, n_2, ...] gives the least common multiple of the n_i.