A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 684000 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 18 19 20 24 25 30 32 36 38 40 45 48 50 57 60 72 75 76 80 90 95 96 100 114 120 125 144 150 152 160 171 180 190 200 225 228 240 250 285 288 300 304 342 360 375 380 400 450 456 475 480 500 570 600 608 684 720 750 760 800 855 900 912 950 1,000 1,125 1,140 1,200 1,368 1,425 1,440 1,500 1,520 1,710 1,800 1,824 1,900 2,000 2,250 2,280 2,375 2,400 2,736 2,850 3,000 3,040 3,420 3,600 3,800 4,000 4,275 4,500 4,560 4,750 5,472 5,700 6,000 6,840 7,125 7,200 7,600 8,550 9,000 9,120 9,500 11,400 12,000 13,680 14,250 15,200 17,100 18,000 19,000 21,375 22,800 27,360 28,500 34,200 36,000 38,000 42,750 45,600 57,000 68,400 76,000 85,500 114,000 136,800 171,000 228,000 342,000 and 684,000, with no remainder.
Since 684,000 cannot be divided by just 1 and 684,000, it is not a prime number.