A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 8500000 can be evenly divided by 1 2 4 5 8 10 16 17 20 25 32 34 40 50 68 80 85 100 125 136 160 170 200 250 272 340 400 425 500 544 625 680 800 850 1,000 1,250 1,360 1,700 2,000 2,125 2,500 2,720 3,125 3,400 4,000 4,250 5,000 6,250 6,800 8,500 10,000 10,625 12,500 13,600 15,625 17,000 20,000 21,250 25,000 31,250 34,000 42,500 50,000 53,125 62,500 68,000 85,000 100,000 106,250 125,000 170,000 212,500 250,000 265,625 340,000 425,000 500,000 531,250 850,000 1,062,500 1,700,000 2,125,000 4,250,000 and 8,500,000, with no remainder.
Since 8,500,000 cannot be divided by just 1 and 8,500,000, it is not a prime number.