A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3880240 can be evenly divided by 1 2 4 5 7 8 10 13 14 16 20 26 28 35 40 41 52 56 65 70 80 82 91 104 112 130 140 164 169 182 205 208 260 280 287 328 338 364 410 455 520 533 560 574 656 676 728 820 845 910 1,040 1,066 1,148 1,183 1,352 1,435 1,456 1,640 1,690 1,820 2,132 2,296 2,366 2,665 2,704 2,870 3,280 3,380 3,640 3,731 4,264 4,592 4,732 5,330 5,740 5,915 6,760 6,929 7,280 7,462 8,528 9,464 10,660 11,480 11,830 13,520 13,858 14,924 18,655 18,928 21,320 22,960 23,660 27,716 29,848 34,645 37,310 42,640 47,320 48,503 55,432 59,696 69,290 74,620 94,640 97,006 110,864 138,580 149,240 194,012 242,515 277,160 298,480 388,024 485,030 554,320 776,048 970,060 1,940,120 and 3,880,240, with no remainder.
Since 3,880,240 cannot be divided by just 1 and 3,880,240, it is not a prime number.