A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1525500 can be evenly divided by 1 2 3 4 5 6 9 10 12 15 18 20 25 27 30 36 45 50 54 60 75 90 100 108 113 125 135 150 180 225 226 250 270 300 339 375 450 452 500 540 565 675 678 750 900 1,017 1,125 1,130 1,350 1,356 1,500 1,695 2,034 2,250 2,260 2,700 2,825 3,051 3,375 3,390 4,068 4,500 5,085 5,650 6,102 6,750 6,780 8,475 10,170 11,300 12,204 13,500 14,125 15,255 16,950 20,340 25,425 28,250 30,510 33,900 42,375 50,850 56,500 61,020 76,275 84,750 101,700 127,125 152,550 169,500 254,250 305,100 381,375 508,500 762,750 and 1,525,500, with no remainder.
Since 1,525,500 cannot be divided by just 1 and 1,525,500, it is not a prime number.