A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 426360 can be evenly divided by 1 2 3 4 5 6 8 10 11 12 15 17 19 20 22 24 30 33 34 38 40 44 51 55 57 60 66 68 76 85 88 95 102 110 114 120 132 136 152 165 170 187 190 204 209 220 228 255 264 285 323 330 340 374 380 408 418 440 456 510 561 570 627 646 660 680 748 760 836 935 969 1,020 1,045 1,122 1,140 1,254 1,292 1,320 1,496 1,615 1,672 1,870 1,938 2,040 2,090 2,244 2,280 2,508 2,584 2,805 3,135 3,230 3,553 3,740 3,876 4,180 4,488 4,845 5,016 5,610 6,270 6,460 7,106 7,480 7,752 8,360 9,690 10,659 11,220 12,540 12,920 14,212 17,765 19,380 21,318 22,440 25,080 28,424 35,530 38,760 42,636 53,295 71,060 85,272 106,590 142,120 213,180 and 426,360, with no remainder.
Since 426,360 cannot be divided by just 1 and 426,360, it is not a prime number.