f(x) = x, unless x = 0 or x = 1/n for some integer n;
f(x) = 1/(n+2) otherwise.
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Now the new one:
Give an example of an infinite sequence a_0, a_1, ... so that the series
infinity
____
\ a_n does not converge, but
/___
n = 0
infinity
____
\ a_n / (1 + n a_n) converges.
/___
n = 0
so that the sequence a looks like this
1, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, ...
The sum of a[i] diverges, but the sum of a[i]/(1+i*a[i]) is 2.
Ed Sheppard
Bellcore