I pass the sample tests or any test that I give myself, but on attempt I'm timing out.
Locally, when I feed my code with lists containing up to 30k numbers it finishes below 12k ms mark.
Is it possible that here the tests on attempt contain unnecessarily huge lists?

I second this.

There should be a clarification in the description that multiples of both 3 and 5 should be included just once in the sum.
For example, 30 = 5 * 6, but also 30 = 3 * 10. The same is for 15, 45, 60, etc. In the current tests those numbers go once in the sum.

Arghhh bummer, for some reason I was reading it as k being the base and 3 the power.
Thank you @Chrono79.

The cube of 1 is 1. So the largest cube of positive integer smaller than 3 is 1 not 0. Therefore largestPower(3) = 0 is incorect. The same goes for N = 2. In case of N = 1, 0 would be the largest cube smaller than 1.

In the exaplanation of the problem there's an example: largestPower(3) = 0, which I think it's untrue.
It should be largestPower(3) = 1.

This was also in the sample tests Test.assert_equals(largestPower(3), 0) and was making the problem impossible to test. If the same test is run on an attempt I think it would never pass.

Can somone look into this?