MathieuCharacteristicExponent[a, q] gives the characteristic exponent r for Mathieu functions with characteristic value a and parameter q.
RamanujanTauTheta[t] gives the Ramanujan tau theta function \[Theta](t).
SphericalBesselJ[n, z] gives the spherical Bessel function of the first kind j_n (z).
SphericalBesselY[n, z] gives the spherical Bessel function of the second kind y_n (z).
SphericalHankelH2[n, z] gives the spherical Hankel function of the second kind h_n^(2)(z).
WeberE
(Built-in Mathematica Symbol) WeberE[\[Nu], z] gives the Weber function E \[Nu] (z).WeberE[\[Nu], \[Mu], z] gives the associated Weber function E_\[Nu]^\[Mu](z).
BSplineBasis[d, x] gives the zeroth uniform B-spline basis function of degree d at x.BSplineBasis[d, n, x] gives the n\[Null]^th uniform B-spline basis function of degree ...
Functions in Mathematica are carefully set up so that you normally do not have to know how they work inside. But particularly for numerical functions that use iterative ...
BernsteinBasis[d, n, x] represents the n\[Null]^th Bernstein basis function of degree d at x.
JacobiND[u, m] gives the Jacobi elliptic function nd(u | m).