A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 3675840 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 64 70 80 84 96 105 112 120 140 160 168 192 210 224 240 280 320 336 420 448 480 547 560 672 840 960 1,094 1,120 1,344 1,641 1,680 2,188 2,240 2,735 3,282 3,360 3,829 4,376 5,470 6,564 6,720 7,658 8,205 8,752 10,940 11,487 13,128 15,316 16,410 17,504 19,145 21,880 22,974 26,256 30,632 32,820 35,008 38,290 43,760 45,948 52,512 57,435 61,264 65,640 76,580 87,520 91,896 105,024 114,870 122,528 131,280 153,160 175,040 183,792 229,740 245,056 262,560 306,320 367,584 459,480 525,120 612,640 735,168 918,960 1,225,280 1,837,920 and 3,675,840, with no remainder.
Since 3,675,840 cannot be divided by just 1 and 3,675,840, it is not a prime number.