Kumar, D., Srivastava, G. S., & Kasana, H. S. (1991). Approximation of entire harmonic functions in \(\mathbb{R}^3\) having index-pair \((p,\,q)\). Anal. Numér. Théor. Approx., 20(1), 47–57. Retrieved from https://ictp.acad.ro/jnaat/journal/article/view/1991-vol20-nos1-2-art7