A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 720000 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 18 20 24 25 30 32 36 40 45 48 50 60 64 72 75 80 90 96 100 120 125 128 144 150 160 180 192 200 225 240 250 288 300 320 360 375 384 400 450 480 500 576 600 625 640 720 750 800 900 960 1,000 1,125 1,152 1,200 1,250 1,440 1,500 1,600 1,800 1,875 1,920 2,000 2,250 2,400 2,500 2,880 3,000 3,200 3,600 3,750 4,000 4,500 4,800 5,000 5,625 5,760 6,000 7,200 7,500 8,000 9,000 9,600 10,000 11,250 12,000 14,400 15,000 16,000 18,000 20,000 22,500 24,000 28,800 30,000 36,000 40,000 45,000 48,000 60,000 72,000 80,000 90,000 120,000 144,000 180,000 240,000 360,000 and 720,000, with no remainder.
Since 720,000 cannot be divided by just 1 and 720,000, it is not a prime number.