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Reciprocal Triangles
Age 16 to 18
Challenge Level 
Prove that the sum of the reciprocals of the first n triangular numbers gets closer and closer to 2 as n grows.
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Telescoping Series
Find S_r = 1^r + 2^r + 3^r + ... + n^r where r is any fixed positive integer in terms of S_1, S_2, ... S_{r-1}.
OK! Now Prove It
Make a conjecture about the sum of the squares of the odd positive integers. Can you prove it?