done

I think that the first line of the instructions would be better phrased as:
'Let be n an integer coprime with 10 e.g. 7.'

The description says to return 'null' in C#, 'None' in Rust, etc. It doesn't say anything about return types in R.

I think your point stands for the 'R' version though, because it is disproportionately difficult in R for an 8 Kyu kata - no beginner R programmer is going to think of the difference in return types between 'return(NULL)' and 'return(NA)'.

I agree with you that the R version really needs a hint to use an 'NA' return type.

My bad - I mixed up Wilson numbers (which include 1) and Wilson primes (which do not).

But 1 is not a prime at all, and Wilson primes are prime numbers with additional restriction. Since 1 is not a prime number, it cannot be a Wilson prime?

In Python the test case P = 1 gives an incorrect result of False.

This should be True.

((P-1)! + 1) / (P * P)
((1-1)! + 1) / (1 * 1)
= ((0)! + 1) / (1 * 1)
= (0! + 1) / 1
= (1 + 1) / 1
= 2 / 1
= 2

Since the result is an integer, P = 1 is a Wilson Prime is True and the test case should pass.