A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 605340 can be evenly divided by 1 2 3 4 5 6 9 10 12 15 18 19 20 27 30 36 38 45 54 57 59 60 76 90 95 108 114 118 135 171 177 180 190 228 236 270 285 295 342 354 380 513 531 540 570 590 684 708 855 885 1,026 1,062 1,121 1,140 1,180 1,593 1,710 1,770 2,052 2,124 2,242 2,565 2,655 3,186 3,363 3,420 3,540 4,484 5,130 5,310 5,605 6,372 6,726 7,965 10,089 10,260 10,620 11,210 13,452 15,930 16,815 20,178 22,420 30,267 31,860 33,630 40,356 50,445 60,534 67,260 100,890 121,068 151,335 201,780 302,670 and 605,340, with no remainder.
Since 605,340 cannot be divided by just 1 and 605,340, it is not a prime number.