Kelvin bei function (imaginary part of BesselJ on a rotated argument).
KelvinBei[z]
KelvinBei[n, z]
KelvinBei[2.5]
→ 1.4571820441598045ReImPlot[KelvinBei[x], {x, 0, 10}, PlotRange -> All]
→ -Graphics-ComplexPlot3D[KelvinBei[2, z], {z, -2 - 2I, 2 + 2I}, PlotLegends -> Automatic]
→ -Graphics3D-