I can't solve too.
Possible solution is (sum - int).
But I'm not sure.
Array is not sorted
Perhaps "Memoization" and "Design Patterns" are actually used.

It is the interesting kata
I have learned a lot of new things

type(result) must be <class 'datetime.datetime'>

'datetime.datetime(2012, 10, 17, 21, 13, 27)' should equal datetime.datetime(2012, 10, 17, 21, 13, 27)

What is the format of the result?

The task solve without sieve of Eratosthenes
Is it right?

The code on the Python
Locally in the worst case with interval 10-1000000 and more it finish for 0.021 seconds
But on the site I get "Timed Out (12000 ms)"
Do I must to find algorithm faster?