Recurrence relations and applications for the Maclaurin coefficients of squared and cubic hypergeometric functions

In this paper, we present and prove that the coefficients $u_n$ and $v_n$ in the series expansions $F^2(a,b;c;z)={\sum }_{n=0}^{\mathrm{\infty }}{u}_n{z}^n$ and $F^3(a,b;c;z)={\sum }_{n=0}^{\mathrm{\infty }}{v}_n{z}^n$ ($a,b,c,z\in \mathbb{C}$ and $-c\mathrm{\notin }\mathbb{N}\cup \{0\}$) satisfy second- and third-order linear recurrence relations, respectively, where $F(a,b;c;x)$ denotes the Gaussian hypergeometric function and $\mathbb{C}$ is the complex plane. Our results provide recurrence relations for the Maclaurin coefficients of the squares and cubes of several classical special functions in the complex domain, including zero-balanced Gauss hypergeometric functions, elliptic integrals, as well as classical orthogonal polynomials such as Chebyshev, Legendre, Gegenbauer, and Jacobi polynomials. As applications, we first establish the monotonicity of a function involving Gauss hypergeometric functions and then present a new proof of the well-known Clausen’s formula.