ChebyshevU[n, x] gives the Chebyshev polynomial of the second kind .
Mathematical function (see Section A.3.10).
Explicit polynomials are given for integer n.
ChebyshevU[n, z] has a branch cut discontinuity in the complex z plane running from to .
See The Mathematica Book: Section 3.2.9.
See also: ChebyshevT.