A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8502720 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 17 20 24 30 32 34 40 48 51 60 64 68 80 85 96 102 120 136 160 170 192 204 240 255 272 320 340 408 480 510 521 544 680 816 960 1,020 1,042 1,088 1,360 1,563 1,632 2,040 2,084 2,605 2,720 3,126 3,264 4,080 4,168 5,210 5,440 6,252 7,815 8,160 8,336 8,857 10,420 12,504 15,630 16,320 16,672 17,714 20,840 25,008 26,571 31,260 33,344 35,428 41,680 44,285 50,016 53,142 62,520 70,856 83,360 88,570 100,032 106,284 125,040 132,855 141,712 166,720 177,140 212,568 250,080 265,710 283,424 354,280 425,136 500,160 531,420 566,848 708,560 850,272 1,062,840 1,417,120 1,700,544 2,125,680 2,834,240 4,251,360 and 8,502,720, with no remainder.
Since 8,502,720 cannot be divided by just 1 and 8,502,720, it is not a prime number.