Riccati equations and convolution formulas for functions of Rayleigh type

N. Kishore, Proc. Amer. Math. Soc. 14 (1963), 523, considered the Rayleigh functions sigma_n, sums of the negative even powers of the (non-zero) zeros of the Bessel function J_nu(z) and provided a convolution type sum formula for finding sigma_n in terms of sigma_1, ...,sigma_{n-1}. His main tool was the recurrence relation for Bessel functions. Here we extend this result to a larger class of functions by using Riccati ifferential equations. We get new results for the zeros of certain combinations of Bessel functions and their first and second derivatives as well as recovering some results of Buchholz for zeros of confluent hypergeometric functions.