A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 573804 can be evenly divided by 1 2 3 4 6 7 9 11 12 14 18 21 22 23 27 28 33 36 42 44 46 54 63 66 69 77 81 84 92 99 108 126 132 138 154 161 162 189 198 207 231 252 253 276 297 308 322 324 378 396 414 462 483 506 567 594 621 644 693 756 759 828 891 924 966 1,012 1,134 1,188 1,242 1,386 1,449 1,518 1,771 1,782 1,863 1,932 2,079 2,268 2,277 2,484 2,772 2,898 3,036 3,542 3,564 3,726 4,158 4,347 4,554 5,313 5,796 6,237 6,831 7,084 7,452 8,316 8,694 9,108 10,626 12,474 13,041 13,662 15,939 17,388 20,493 21,252 24,948 26,082 27,324 31,878 40,986 47,817 52,164 63,756 81,972 95,634 143,451 191,268 286,902 and 573,804, with no remainder.
Since 573,804 cannot be divided by just 1 and 573,804, it is not a prime number.