I just started reading about friendly numbers and I think they sound great.
In number theory, friendly numbers are two or more natural numbers with a common abundancy, the ratio between the sum of divisors of a number and the number itself. Two numbers with the same abundancy form a friendly pair; n numbers with the same abundancy form a friendly n-tuple.
So, how small a program can you write to output a list of the first 20 friendly numbers.
Assuming I've understood everything I've read correctly the output of your program should be:
6,28 30,140 80,200 40,224 12,234 84,270 66,308 78,364 102,476 6,496 28,496 114,532 240,600 138,644 120,672 150,700 174,812 135,819 186,868 864,936 222,1036 246,1148
I'd also like to add that the program must calculate the answers and not use any external resources or hard coded answers (thanks Peter).