The Cunningham function, sometimes also called the Pearson-Cunningham function, can be expressed using Whittaker functions (Whittaker and Watson 1990, p. 353).
where confluent hypergeometric function of the second kind (Abramowitz and Stegun 1972, p. 510).
See also Confluent Hypergeometric Function of the Second Kind ,
Whittaker Function Explore with Wolfram|Alpha References Abramowitz, M. and Stegun, I. A. (Eds.). Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing. Whittaker, E. T. and Watson, G. N. A Course in Modern Analysis, 4th ed. Referenced on Wolfram|Alpha Cunningham Function Cite this as: Weisstein, Eric W. "Cunningham Function." From MathWorld https://mathworld.wolfram.com/CunninghamFunction.html
Subject classifications 
is a confluent hypergeometric function of the second kind (Abramowitz and Stegun 1972, p. 510). 