
 Primitive_recursive_function (Site not responding. Last check: 20071105) 
  In computability theory, '''primitive recursive functions''' are a class of functions which form an important building block on the way to a full formalization of computability. 
  Many of the functions normally studied in number theory, and approximations to realvalued functions, are primitive recursive, such as addition, division, factorial, exponential, finding the ''n''th prime, and so on (Brainerd and Landweber, 1974). 
  Many other familiar functions can be shown to be primitive recursive; some examples include conditionals, exponentiation, primality testing, and mathematical induction, and the primitive recursive functions can be extended to operate on other objects such as integers and rational numbers. 
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