Differential equations for the elementary 3-symmetric Chebyshev polynomials

We continue the study of “composed model of generalized oscillator” and related simplest 3-symmetric Chebyshev polynomials. For this polynomials we obtain the second order differential equations which are of the fuchsian type. These equations have 13 singular points. The obtained results gives (in the considered simplest case) the answer on the more general question. What changes appears in the differential equations for polynomials of the Askey–Wilson scheme when the Jacobi matrix related with these polynomials was distributed by diagonal matrix with complex diagonal.