© 1986 by London Mathematical Society
An Integral of Products of Ultraspherical Functions and a q-Extension
Department of Mathematics, University of Wisconsin Madison 53706, USA
Centre for Mathematics and Computer Science PO Box 4079, 1009 AB, Amsterdam, Netherlands
Department of Mathematics and Statistics, Carleton University Ottawa, Ontario, Canada K1S 5B6
Let Pn(x) and Qn{x) denote the Legendre polynomial of degree n and the usual second solution to the differential equation, respectively. Din showed that
vanishes when |lm| < n < l+m, and Askey evaluated the integral for arbitrary integral values ofl, m and n. We extend this to the evaluation of
, where
is the ultraspherical polynomial and C
n(x) is the appropriate second solution to the ultraspherical differential equation. A q-extension is found using the continuous q-ultraspherical polynomials of Rogers. Again the integral vanishes when |lm| < n < l+m. It is shown that this vanishing phenomenon holds for quite general orthogonal polynomials. A related integral of the product of three Bessel functions is also evaluated.