A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1260504 can be evenly divided by 1 2 3 4 6 7 8 9 12 14 18 21 24 28 36 41 42 56 61 63 72 82 84 122 123 126 164 168 183 244 246 252 287 328 366 369 427 488 492 504 549 574 732 738 854 861 984 1,098 1,148 1,281 1,464 1,476 1,708 1,722 2,196 2,296 2,501 2,562 2,583 2,952 3,416 3,444 3,843 4,392 5,002 5,124 5,166 6,888 7,503 7,686 10,004 10,248 10,332 15,006 15,372 17,507 20,008 20,664 22,509 30,012 30,744 35,014 45,018 52,521 60,024 70,028 90,036 105,042 140,056 157,563 180,072 210,084 315,126 420,168 630,252 and 1,260,504, with no remainder.
Since 1,260,504 cannot be divided by just 1 and 1,260,504, it is not a prime number.