Computable Functions

1. The Busy Beaver functions
   1. Wikipedia’s page
   2. Mathword's Page
   3. Heiner Marxen’s page with the current status of many efforts to determine values for busy-beaverones (Rado’s S function)
   4. Michael Somos’s page with a bibliography
   5. The quadruple version of the problem (in which a Turing machine may either write o
   6. Historical survey of busy beaver results for several variants of the problem

Recursive Function Theory

1. Ackermann’s function
   1. Mathworld’s page
   2. Wikipedia’s page

The Recursion Theorem and its Use