A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 4200300 can be evenly divided by 1 2 3 4 5 6 9 10 12 13 15 18 20 25 26 30 36 39 45 50 52 60 65 75 78 90 100 117 130 150 156 180 195 225 234 260 300 325 359 390 450 468 585 650 718 780 900 975 1,077 1,170 1,300 1,436 1,795 1,950 2,154 2,340 2,925 3,231 3,590 3,900 4,308 4,667 5,385 5,850 6,462 7,180 8,975 9,334 10,770 11,700 12,924 14,001 16,155 17,950 18,668 21,540 23,335 26,925 28,002 32,310 35,900 42,003 46,670 53,850 56,004 64,620 70,005 80,775 84,006 93,340 107,700 116,675 140,010 161,550 168,012 210,015 233,350 280,020 323,100 350,025 420,030 466,700 700,050 840,060 1,050,075 1,400,100 2,100,150 and 4,200,300, with no remainder.
Since 4,200,300 cannot be divided by just 1 and 4,200,300, it is not a prime number.