In three dimensions, the spherical harmonic differential equation is given by
and solutions are called spherical harmonics (Zwillinger 1997, p. 130). In four dimensions, the spherical harmonic differential equation is
(Humi 1987; Zwillinger 1997, p. 130).
More things to try:
Weisstein, Eric W. "Spherical Harmonic Differential Equation." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SphericalHarmonicDifferentialEquation.html
![[1/(sintheta)partial/(partialtheta)(sinthetapartial/(partialtheta))+1/(sin^2theta)(partial^2)/(partialphi^2)+l(l+1)]u=0,](/images/equations/SphericalHarmonicDifferentialEquation/NumberedEquation1.svg)
