| 
 | 
 | 
A Hypergeometric Function in which one parameter changes by +1 or 
 is said to be contiguous.  There are 26
functions contiguous to 
 taking one pair at a time.  There are 325 taking two or more pairs at a time.
See Abramowitz and Stegun (1972, pp. 557-558). 
See also Hypergeometric Function
References
Abramowitz, M. and Stegun, C. A. (Eds.).
  Handbook of Mathematical Functions with Formulas, Graphs, and Mathematical Tables, 9th printing.
  New York: Dover, 1972.