A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 4205124 can be evenly divided by 1 2 3 4 6 7 9 11 12 14 18 21 22 28 33 36 37 41 42 44 63 66 74 77 82 84 99 111 123 126 132 148 154 164 198 222 231 246 252 259 287 308 333 369 396 407 444 451 462 492 518 574 666 693 738 777 814 861 902 924 1,036 1,148 1,221 1,332 1,353 1,386 1,476 1,517 1,554 1,628 1,722 1,804 2,331 2,442 2,583 2,706 2,772 2,849 3,034 3,108 3,157 3,444 3,663 4,059 4,551 4,662 4,884 5,166 5,412 5,698 6,068 6,314 7,326 8,118 8,547 9,102 9,324 9,471 10,332 10,619 11,396 12,628 13,653 14,652 16,236 16,687 17,094 18,204 18,942 21,238 25,641 27,306 28,413 31,857 33,374 34,188 37,884 42,476 50,061 51,282 54,612 56,826 63,714 66,748 95,571 100,122 102,564 113,652 116,809 127,428 150,183 191,142 200,244 233,618 300,366 350,427 382,284 467,236 600,732 700,854 1,051,281 1,401,708 2,102,562 and 4,205,124, with no remainder.
Since 4,205,124 cannot be divided by just 1 and 4,205,124, it is not a prime number.