This number is a prime.
The prime 616841 marks the second time the count of primes 1 mod 4 exceeds the count of primes 3 mod 4 (counts are 25189 vs 25188). Documented by actual count and by Hans Riesel, Prime numbers and computer methods for factorization, 2nd ed. (Boston, Birkhauser: 1994), p 76. [Haga]