A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 811680 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 19 20 24 30 32 38 40 48 57 60 76 80 89 95 96 114 120 152 160 178 190 228 240 267 285 304 356 380 445 456 480 534 570 608 712 760 890 912 1,068 1,140 1,335 1,424 1,520 1,691 1,780 1,824 2,136 2,280 2,670 2,848 3,040 3,382 3,560 4,272 4,560 5,073 5,340 6,764 7,120 8,455 8,544 9,120 10,146 10,680 13,528 14,240 16,910 20,292 21,360 25,365 27,056 33,820 40,584 42,720 50,730 54,112 67,640 81,168 101,460 135,280 162,336 202,920 270,560 405,840 and 811,680, with no remainder.
Since 811,680 cannot be divided by just 1 and 811,680, it is not a prime number.