A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1548960 can be evenly divided by 1 2 3 4 5 6 7 8 10 12 14 15 16 20 21 24 28 30 32 35 40 42 48 56 60 70 80 84 96 105 112 120 140 160 168 210 224 240 280 336 420 461 480 560 672 840 922 1,120 1,383 1,680 1,844 2,305 2,766 3,227 3,360 3,688 4,610 5,532 6,454 6,915 7,376 9,220 9,681 11,064 12,908 13,830 14,752 16,135 18,440 19,362 22,128 25,816 27,660 32,270 36,880 38,724 44,256 48,405 51,632 55,320 64,540 73,760 77,448 96,810 103,264 110,640 129,080 154,896 193,620 221,280 258,160 309,792 387,240 516,320 774,480 and 1,548,960, with no remainder.
Since 1,548,960 cannot be divided by just 1 and 1,548,960, it is not a prime number.