The complexity of the problem as stated is worst case O(n^3) in the magnitude of the greatest value a[i]. The reason being that it is a simple sum, as stated, of square roots. The square root operation is O(n^2) in the number of bits, which has a 3.xxx:1 relation to the magnitude of each a[i]. Either the problem is mistated or it has not been significant enough for anyone to waste time on stating the obvious.
Complexity
The complexity of the problem as stated is worst case O(n^3) in the magnitude of the greatest value a[i]. The reason being that it is a simple sum, as stated, of square roots. The square root operation is O(n^2) in the number of bits, which has a 3.xxx:1 relation to the magnitude of each a[i]. Either the problem is mistated or it has not been significant enough for anyone to waste time on stating the obvious.