A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1320960 can be evenly divided by 1 2 3 4 5 6 8 10 12 15 16 20 24 30 32 40 43 48 60 64 80 86 96 120 128 129 160 172 192 215 240 256 258 320 344 384 430 480 512 516 640 645 688 768 860 960 1,024 1,032 1,280 1,290 1,376 1,536 1,720 1,920 2,048 2,064 2,560 2,580 2,752 3,072 3,440 3,840 4,128 5,120 5,160 5,504 6,144 6,880 7,680 8,256 10,240 10,320 11,008 13,760 15,360 16,512 20,640 22,016 27,520 30,720 33,024 41,280 44,032 55,040 66,048 82,560 88,064 110,080 132,096 165,120 220,160 264,192 330,240 440,320 660,480 and 1,320,960, with no remainder.
Since 1,320,960 cannot be divided by just 1 and 1,320,960, it is not a prime number.