Weak (or non-existent) test cases in AlgoFlux19.1's "Let's Play A Game"?

In the question PRMGM, many accepted solutions (such as this and this) fail for a simple test case. These solutions have ignored the prime numbers and yet managed to somehow get an AC verdict!

1
2
2 3

Or did I interpret the question incorrectly? Although a few accepted solutions like this one do give the opposite output.

Yes, you are correct , i myself have analysed many solution which are not giving the answers as expected .
Few of them are:

1.solution_1 Test Case:1 5 2 2 3 5 7
2. solution_2 Test Case:1 4 5 3 7 2

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