A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1607520 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 17 20 24 30 32 34 40 48 51 60 68 80 85 96 102 120 136 160 170 197 204 240 255 272 340 394 408 480 510 544 591 680 788 816 985 1,020 1,182 1,360 1,576 1,632 1,970 2,040 2,364 2,720 2,955 3,152 3,349 3,940 4,080 4,728 5,910 6,304 6,698 7,880 8,160 9,456 10,047 11,820 13,396 15,760 16,745 18,912 20,094 23,640 26,792 31,520 33,490 40,188 47,280 50,235 53,584 66,980 80,376 94,560 100,470 107,168 133,960 160,752 200,940 267,920 321,504 401,880 535,840 803,760 and 1,607,520, with no remainder.
Since 1,607,520 cannot be divided by just 1 and 1,607,520, it is not a prime number.