A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1403520 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 17 20 24 30 32 34 40 43 48 51 60 64 68 80 85 86 96 102 120 128 129 136 160 170 172 192 204 215 240 255 258 272 320 340 344 384 408 430 480 510 516 544 640 645 680 688 731 816 860 960 1,020 1,032 1,088 1,290 1,360 1,376 1,462 1,632 1,720 1,920 2,040 2,064 2,176 2,193 2,580 2,720 2,752 2,924 3,264 3,440 3,655 4,080 4,128 4,386 5,160 5,440 5,504 5,848 6,528 6,880 7,310 8,160 8,256 8,772 10,320 10,880 10,965 11,696 13,760 14,620 16,320 16,512 17,544 20,640 21,930 23,392 27,520 29,240 32,640 35,088 41,280 43,860 46,784 58,480 70,176 82,560 87,720 93,568 116,960 140,352 175,440 233,920 280,704 350,880 467,840 701,760 and 1,403,520, with no remainder.
Since 1,403,520 cannot be divided by just 1 and 1,403,520, it is not a prime number.