Recursive demos:
comma2		print 2,345,767,090,987 (with error, zeroes not properly handled)
comma           corrects comma2.
demorecurse     returns the sum of n's digits.
printdown       print digits in a column
recursive       calculates k-th largest. Demonstrates both O(n) and O(n^2)
remember        calculate the number of ways n can be written as a sum of k positive integers with the remeber option.