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One of the challenges of this problem is the reading of a mathematical text for understanding
It would be interesting to investigate why superincreasing series are easier to deal with.
There is an article on Knapsack codes.
a) A four digit number (in base 10) aabb is a perfect square. Discuss ways of systematically finding this number. (b) Prove that 11^{10}-1 is divisible by 100.