Let p be a Mersenne prime. We have shown that the Diophantine equation
px + (p + 1)y = z2 has no solution except for p = 3, 7. Note that the results in
[3] and [4] are special cases of our theorem since 7 and 31 are Mersenne primes.
Nevertheless, the Diophantine equation px + (p + 1)y = z2 where p is not a
Mersenne prime remains an open problem.