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Not too much (Posted on 2015-02-20) Difficulty: 2 of 5
What is the sum of the reciprocals of all the nonzero
triangular numbers?

No Solution Yet Submitted by Ady TZIDON    
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spoiler and telescoping sums | Comment 1 of 8
We need to find limit of the sum (1/(n * (n+1)) = limit(1/n - 1/(n+1) = limit( (1-1/2) + (1/2 - 1/3) + (1/3 - 1/4) . . . ) = 1.

The required number is twice that or 2.

  Posted by xdog on 2015-02-20 10:00:18
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