A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 7847040 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 20 24 30 32 40 48 60 61 64 67 80 96 120 122 128 134 160 183 192 201 240 244 268 305 320 335 366 384 402 480 488 536 610 640 670 732 804 915 960 976 1,005 1,072 1,220 1,340 1,464 1,608 1,830 1,920 1,952 2,010 2,144 2,440 2,680 2,928 3,216 3,660 3,904 4,020 4,087 4,288 4,880 5,360 5,856 6,432 7,320 7,808 8,040 8,174 8,576 9,760 10,720 11,712 12,261 12,864 14,640 16,080 16,348 19,520 20,435 21,440 23,424 24,522 25,728 29,280 32,160 32,696 39,040 40,870 42,880 49,044 58,560 61,305 64,320 65,392 81,740 98,088 117,120 122,610 128,640 130,784 163,480 196,176 245,220 261,568 326,960 392,352 490,440 523,136 653,920 784,704 980,880 1,307,840 1,569,408 1,961,760 2,615,680 3,923,520 and 7,847,040, with no remainder.
Since 7,847,040 cannot be divided by just 1 and 7,847,040, it is not a prime number.