A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 839520 can be evenly divided by 1 2 3 4 5 6 8 9 10 11 12 15 16 18 20 22 24 30 32 33 36 40 44 45 48 53 55 60 66 72 80 88 90 96 99 106 110 120 132 144 159 160 165 176 180 198 212 220 240 264 265 288 318 330 352 360 396 424 440 477 480 495 528 530 583 636 660 720 792 795 848 880 954 990 1,056 1,060 1,166 1,272 1,320 1,440 1,584 1,590 1,696 1,749 1,760 1,908 1,980 2,120 2,332 2,385 2,544 2,640 2,915 3,168 3,180 3,498 3,816 3,960 4,240 4,664 4,770 5,088 5,247 5,280 5,830 6,360 6,996 7,632 7,920 8,480 8,745 9,328 9,540 10,494 11,660 12,720 13,992 15,264 15,840 17,490 18,656 19,080 20,988 23,320 25,440 26,235 27,984 34,980 38,160 41,976 46,640 52,470 55,968 69,960 76,320 83,952 93,280 104,940 139,920 167,904 209,880 279,840 419,760 and 839,520, with no remainder.
Since 839,520 cannot be divided by just 1 and 839,520, it is not a prime number.