A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1872640 can be evenly divided by 1 2 4 5 7 8 10 11 14 16 19 20 22 28 32 35 38 40 44 55 56 64 70 76 77 80 88 95 110 112 128 133 140 152 154 160 176 190 209 220 224 256 266 280 304 308 320 352 380 385 418 440 448 532 560 608 616 640 665 704 760 770 836 880 896 1,045 1,064 1,120 1,216 1,232 1,280 1,330 1,408 1,463 1,520 1,540 1,672 1,760 1,792 2,090 2,128 2,240 2,432 2,464 2,660 2,816 2,926 3,040 3,080 3,344 3,520 4,180 4,256 4,480 4,864 4,928 5,320 5,852 6,080 6,160 6,688 7,040 7,315 8,360 8,512 8,960 9,856 10,640 11,704 12,160 12,320 13,376 14,080 14,630 16,720 17,024 19,712 21,280 23,408 24,320 24,640 26,752 29,260 33,440 34,048 42,560 46,816 49,280 53,504 58,520 66,880 85,120 93,632 98,560 117,040 133,760 170,240 187,264 234,080 267,520 374,528 468,160 936,320 and 1,872,640, with no remainder.
Since 1,872,640 cannot be divided by just 1 and 1,872,640, it is not a prime number.