A prime number is a natural number, greater than one, that can only be divided by 1 and itself.
The number 1872720 can be evenly divided by 1 2 3 4 5 6 8 9 10 12 15 16 17 18 20 24 27 30 34 36 40 45 48 51 54 60 68 72 80 81 85 90 102 108 120 135 136 144 153 162 170 180 204 216 240 255 270 272 289 306 324 340 360 405 408 432 459 510 540 578 612 648 680 720 765 810 816 867 918 1,020 1,080 1,156 1,224 1,296 1,360 1,377 1,445 1,530 1,620 1,734 1,836 2,040 2,160 2,295 2,312 2,448 2,601 2,754 2,890 3,060 3,240 3,468 3,672 4,080 4,335 4,590 4,624 5,202 5,508 5,780 6,120 6,480 6,885 6,936 7,344 7,803 8,670 9,180 10,404 11,016 11,560 12,240 13,005 13,770 13,872 15,606 17,340 18,360 20,808 22,032 23,120 23,409 26,010 27,540 31,212 34,680 36,720 39,015 41,616 46,818 52,020 55,080 62,424 69,360 78,030 93,636 104,040 110,160 117,045 124,848 156,060 187,272 208,080 234,090 312,120 374,544 468,180 624,240 936,360 and 1,872,720, with no remainder.
Since 1,872,720 cannot be divided by just 1 and 1,872,720, it is not a prime number.