604

604 = 2² x 151.

604 is a number that cannot be written as a sum of three squares.

604 and the two numbers before it and after it are all products of exactly three primes: 602 = 2 x 7 x 43; 603 = 3 x 3 x 67; 604 = 2 x 2 x 151; 605 = 5 x 11 x 11; 606 = 2 x 3 x 101.

604 is 2444 in base 6 and 424 in base 12.

Nebula NGC 604 was discovered by William Herschel in 1784. It is 3 million light years away. Note that 604 x 1784 + 3 is prime.

Source: Prime Curios!