Question

Here's your math challenge of the day. Let (a_n) be a sequence of positive real numbers, decreasing and the sum of whose terms are infinite. Prove that the series whose general term is min(a_n) is also divergent.

Taken from AoPS, and by extension, the German TST.

It's a pretty problem.

Answer 1

Sorry, I mean min(a_n, 1/n)

Answer 2

X3 bad typo

Answer 3

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