primes of the form (p^q-q^p)/2 bad syntax?

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@rburing

I suppose it is a bug that fNum.is_prime() generates an error ?

var('p,q',domain='integer')
f=(p^q-q^p)/2
for pV in range(1,10):
    for qV in range(1,10):
        pV=Integer(pV) ; qV=Integer(qV)
        fNum=f.subs(p=pV,q=qV)
        if pV.is_prime() and qV.is_prime()  :
            if fNum.is_integer() and fNum.is_positive() :
                show(fNum," \t p : \t ",pV," \t q : \t ",qV)
                #show(fNum.is_prime())

@ortollj The error shows that the is_prime method of a symbolic expression (here: fNum) does not have a sensible implementation. I would consider it mostly expected, though I would probably prefer an immediate NotImplementedError. You can do Integer(fNum).is_prime(), after checking e.g. fNum.is_integer().

OK, but it is a bit weird that after testing with success fNum is integer ,we need to cast it as Integer ? because fNum.is_integer()=True tell us it is an Integer !