A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8640000 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 18 20 24 25 27 30 32 36 40 45 48 50 54 60 64 72 75 80 90 96 100 108 120 125 128 135 144 150 160 180 192 200 216 225 240 250 256 270 288 300 320 360 375 384 400 432 450 480 500 512 540 576 600 625 640 675 720 750 768 800 864 900 960 1,000 1,080 1,125 1,152 1,200 1,250 1,280 1,350 1,440 1,500 1,536 1,600 1,728 1,800 1,875 1,920 2,000 2,160 2,250 2,304 2,400 2,500 2,560 2,700 2,880 3,000 3,200 3,375 3,456 3,600 3,750 3,840 4,000 4,320 4,500 4,608 4,800 5,000 5,400 5,625 5,760 6,000 6,400 6,750 6,912 7,200 7,500 7,680 8,000 8,640 9,000 9,600 10,000 10,800 11,250 11,520 12,000 12,800 13,500 13,824 14,400 15,000 16,000 16,875 17,280 18,000 19,200 20,000 21,600 22,500 23,040 24,000 27,000 28,800 30,000 32,000 33,750 34,560 36,000 38,400 40,000 43,200 45,000 48,000 54,000 57,600 60,000 64,000 67,500 69,120 72,000 80,000 86,400 90,000 96,000 108,000 115,200 120,000 135,000 144,000 160,000 172,800 180,000 192,000 216,000 240,000 270,000 288,000 320,000 345,600 360,000 432,000 480,000 540,000 576,000 720,000 864,000 960,000 1,080,000 1,440,000 1,728,000 2,160,000 2,880,000 4,320,000 and 8,640,000, with no remainder.
Since 8,640,000 cannot be divided by just 1 and 8,640,000, it is not a prime number.