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.
HypergeometricU[a, b, z] is the confluent hypergeometric function U(a, b, z).
LCM
(Built-in Mathematica Symbol) LCM[n_1, n_2, ...] gives the least common multiple of the n_i.
LegendreQ[n, z] gives the Legendre function of the second kind Q_n (z). LegendreQ[n, m, z] gives the associated Legendre function of the second kind Q_n^m(z).
LogIntegral[z] is the logarithmic integral function li(z).
ModularLambda[\[Tau]] gives the modular lambda elliptic function \[Lambda](\[Tau]).
NorlundB[n, a] gives Nørlund polynomials B_n^(a) of degree n in a.NorlundB[n, a, x] gives generalized Bernoulli polynomials B_n^(a)(x).
Quotient[m, n] gives the integer quotient of m and n. Quotient[m, n, d] uses an offset d.
RamanujanTau[n] gives the Ramanujan \[Tau] function \[Tau](n).