A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3120480 can be evenly divided by 1 2 3 4 5 6 8 9 10 11 12 15 16 18 20 22 24 30 32 33 36 40 44 45 48 55 60 66 72 80 88 90 96 99 110 120 132 144 160 165 176 180 197 198 220 240 264 288 330 352 360 394 396 440 480 495 528 591 660 720 788 792 880 985 990 1,056 1,182 1,320 1,440 1,576 1,584 1,760 1,773 1,970 1,980 2,167 2,364 2,640 2,955 3,152 3,168 3,546 3,940 3,960 4,334 4,728 5,280 5,910 6,304 6,501 7,092 7,880 7,920 8,668 8,865 9,456 10,835 11,820 13,002 14,184 15,760 15,840 17,336 17,730 18,912 19,503 21,670 23,640 26,004 28,368 31,520 32,505 34,672 35,460 39,006 43,340 47,280 52,008 56,736 65,010 69,344 70,920 78,012 86,680 94,560 97,515 104,016 130,020 141,840 156,024 173,360 195,030 208,032 260,040 283,680 312,048 346,720 390,060 520,080 624,096 780,120 1,040,160 1,560,240 and 3,120,480, with no remainder.
Since 3,120,480 cannot be divided by just 1 and 3,120,480, it is not a prime number.