A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1397280 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 20 24 30 32 40 41 48 60 71 80 82 96 120 123 142 160 164 205 213 240 246 284 328 355 410 426 480 492 568 615 656 710 820 852 984 1,065 1,136 1,230 1,312 1,420 1,640 1,704 1,968 2,130 2,272 2,460 2,840 2,911 3,280 3,408 3,936 4,260 4,920 5,680 5,822 6,560 6,816 8,520 8,733 9,840 11,360 11,644 14,555 17,040 17,466 19,680 23,288 29,110 34,080 34,932 43,665 46,576 58,220 69,864 87,330 93,152 116,440 139,728 174,660 232,880 279,456 349,320 465,760 698,640 and 1,397,280, with no remainder.
Since 1,397,280 cannot be divided by just 1 and 1,397,280, it is not a prime number.