A perfect number is a number for which the sum of its proper divisors is exactly equal to the number. For example, the sum of the proper divisors of 28 would be 1 + 2 + 4 + 7 + 14 = 28, which means that 28 is a perfect number.

Starting with the number 1 and moving to the right in a clockwise direction a 5 by 5 spiral is formed as follows:

Consider all integer combinations of ab for 2 a 5 and 2 b 5:

Work out the first ten digits of the sum of the following one-hundred 50-digit numbers.

The following iterative sequence is defined for the set of positive integers: