problems = {HoldForm[GeneratingFunction[UnitStep[n + 1/2], n, z]],
HoldForm[GeneratingFunction[n^2 + 2, n, z]],
HoldForm[GeneratingFunction[1/(2 n + 1), n, z]],
HoldForm[GeneratingFunction[Sin[a n], n, z]],
HoldForm[GeneratingFunction[ChebyshevU[n, a], n, z]],
HoldForm[GeneratingFunction[BernoulliB[n]/n!, n, z]],
HoldForm[GeneratingFunction[a^n Sin[n], n, z]],
HoldForm[GeneratingFunction[Mod[n, 7], n, z]],
HoldForm[GeneratingFunction[f[n + 1], n, z]],
HoldForm[GeneratingFunction[Binomial[m, n], {m, n}, {u, v}]],
HoldForm[GeneratingFunction[m/(n + 1), {m, n}, {u, v}]]};